GETTING INTO BUTTERFLIES
Everyone knows what a butterfly is when he or she sees one and
most people could identify many butterflies to species by utilizing appropriate
color pictures. Indeed, when observing
an organism, the first question usually asked is “what is it?”. One of the primary purposes of this book is
to answer that question. Yet, there is
much more to a butterfly (or any organism) than the name assigned to it. Glancing through this book, this should be
readily apparent. Butterflies undergo
radical transformations in their development from egg to adult. Many butterflies are found in very specific
habitats; others are generally distributed.
Some butterflies migrate; others never leave the spot where they spent
their immature lives. An interest in
butterflies truly begins rather than ends with knowledge of their
identity. The purpose of this chapter is
to introduce some of the terms found in the text of the book and also to
summarize a few of the interesting biological, behavioral, and structural
attributes of butterflies. Most of the
butterfly species to be mentioned are
Preliminary Remarks
What is a butterfly?
All butterflies are insects. All insects have six legs and an external skeleton (referred to as the exoskeleton). The butterfly body is divided into three parts; head, thorax, and abdomen. The six legs and four wings are attached to the thorax. A pair of clubbed antennae originates from the butterfly head.
Butterflies belong to the “order” (a classification category) Lepidoptera. The word “Lepidoptera” is derived from the Latin words lepido (meaning “scale”), and ptera (meaning “wings”). Thus, Lepidoptera literally means “scale wings”, referring to the minute scale-like structures on the wings of both butterflies and moths, which comprise this order.
A butterfly is basically a day-flying lepidopteran. This characteristic does not by itself separate butterflies from moths, since there are many day-flying moths as well.
Butterflies generally differ from moths in several other ways. The butterfly antenna generally ends in a well-defined club, whereas moth antennae are thread-like or feathery in nature. Moth bodies are generally quite robust; butterfly bodies are generally slender. Moths generally rest with their wings spread flat; resting butterflies usually have their wings folded above the body and against each other. “Skippers” seem to be neither butterflies nor moths, the skipper antennae ends in a semiclub. When at rest, a skipper often holds the hind wings flat and the forewings above the body. These are only a few of the characteristics which place skippers apart from true butterflies and in fact, they are placed in a separate superfamily (Hesperioidea) from other North American butterflies, which are placed in the Papilionoidea. The true butterflies and skippers collectively make up the suborder Rhopalocera.
What is a lepidopterist?
Entomologists are those who study insects, whereas Lepidopterists are entomologists who study butterflies and/or moths. Lepidopterists may or may not be butterfly collectors, and the more serious lepidopterists probably spend more time studying dead butterflies and/or observing live butterflies than they spend collecting them. Some lepidopterists concentrate on rearing butterflies. The “hows” of butterfly collecting are best learned through reading the introductory chapters in Ehrlich and Ehrlich (1961). Photography is becoming increasingly popular in the study of all insects for recording their behavior; basic techniques and equipment needed for butterfly photography may be found in Pyle (1974).
Classification
Approximately 700 species of butterflies are known from North
America north of
To summarize and complete the picture, a “species” may be divided into two or more “subspecies”. Related “species” are grouped into “genera” (singular, “genus”). Related genera are grouped into “families”, related “families” are grouped into “orders” and so on. To give an example, the Monarch Butterfly belongs to the kingdom Animalia, the phylum Arthropoda, the class Insecta, the order Lepidoptera, the family Danaidae, the genus Danaus and the species plexippus.
Latin or scientific names
Throughout this book and in almost any natural history identification guide, one finds strange words, usually grouped in twos or threes, and either underlined or italicized. These are the scientific or Latin names; each species and subspecies in the animal and the plant kingdom is assigned a unique scientific name. This is why scientific names are superior to common names, since more than one common name will often exist for one species.
A typical scientific name follows:
Apodemia mormo virgulti (Behr)
The first Latin word is the name of the genus. This particular genus, Apodemia, has about nine species assigned to it (Powell, 1975). In this example, we refer to the species mormo--the second Latin word in the scientific name. The third Latin word is the name of the subspecies. Although the species mormo may be found throughout the western United States and south into Baja California, the subspecies virgulti occurs only in southern California, and south into adjacent Mexico. The last word in the scientific name (which is in parenthesis in this example) is the name of the individual who described that species or subspecies. Dr. Hans Behr, a 19th Century lepidopterist, described the subspecies virgulti. However, Behr placed virgulti in a genus other than the one to which it is presently assigned. It is for this reason that Dr. Behr’s name is in parentheses. If, instead, Behr had described virgulti as a member of Apodemia (i.e., the genus to which it is currently assigned), then his name would not be in parentheses. The author's name is usually given the first time a scientific name is mentioned in a text (also usually included in checklists of scientific names), but is more often absent in subsequent citations.
Hybrids
Although, as we mentioned earlier, different species are considered reproductively isolated, there are exceptions to our definition. Hybrids occasionally occur as a result of mating between similar species. Such hybrids often occur, for example, between closely related species in the genus Limenitis (family Nymphalidae) (see Perkins and Garth, 1972; Platt and Greenfield, 1971), or in the genus Colias (family Pieridae) (see Priestaff, 1974). These occurrences may actually indicate two groups of populations that have only recently evolved to the point where they can be considered a separate species. Hybrids are usually sterile, however, producing no offspring.
Variation and Aberration
Obviously, there can often be great differences in appearance between individuals of two species; likewise some consistent differences are also found between two valid sub-species. Even within a single population one can often find individual variation. Some examples of butterfly variation (also known as aberrations) are given below.
Very rarely one finds “one-of-a-kind” variations or comes across variations or aberrations that pop up again and again in a population, but always in very low frequencies (as low as .00023; see Shapiro, 1974a). The aberrations found in species of the genus Cynthia (pages 126-31) are fairly well known (Shapiro, 1973) although the causes of such recurrent “freaks” are not always known. One variation of the Painted Lady Butterfly (Cynthia cardui) known as “elmi” can be induced by holding fresh pupae at low temperatures (36oF) for two weeks (Dimock, 1968; Shapiro, 1974a). Comstock (1927) in reporting variations of the Buckeye Butterfly (Precis lavinia coenia), noted that the “eyespots” on the wings tend to be abnormally large in specimens reared in moist, warm chambers; exposure to a dry, warm environment produces abnormally small “eyespots”. Some lepidopterists believe that constant color pattern differences between two subspecies of the same species may simply be the result of the different environments in which they live (for example, Plebejus icarioides). Exposure to high solar radiation (e.g. in deserts) may produce individuals possessing exceptionally light coloration. Other climatic differences might also affect wing pattern coloration, although this needs documentation.
Gynandromorphs
A very rare type of aberration is the gynandromorph (individuals which are part male and part female). Such individuals are more easily recognized when wing patterns normally differ between the sexes. A bilateral gynandromorph is an individual that is half male, half female. In bilateral gynandromorph butterflies, the left wings exhibit the color pattern typical of one sex, while the right wings show the color pattern of the opposite sex. A gynandromorph Acmon Blue (Plebejus acmon) butterfly, for example, might have brown left wings (female) and iridescent blue right wings (male). Gynandromorphs are caused by the loss of one of the two sex chromosomes in a cell during development (often when the butterfly embryo consists of just one or two cells). At present, it is not clearly understood just what is responsible for the chromosome loss in butterflies. Figures of bilateral or near-bilateral gynandromorphs may be seen in Opler (1966) (color plate), Perkins and Perkins (1973), and Shapiro (1970a).
Seasonal Variation
Some butterflies undergo predictable pattern variation over time. This seasonal variation occurs in several Orange County butterflies, notably those within the family Pieridae.
The Alfalfa Caterpillar Butterfly (Colias, eurytheme , for example, has a spring and a summer-form, each distinguishable from the other by the varying amounts of yellow or orange present (the summer brood has more orange). Other Orange County butterflies undergoing seasonal variation include the Sara Orange-Tip (Anthocaris sara and the California Ringlet (Coenonympha california). These seasonal variations are not genetically based, but rather are induced by the changing environmental conditions to which the butterfly larva and/or pupa of each brood is exposed.
At one time, many variations, “forms” and aberrations received Latin names. Such names cluttered up the literature and none are currently considered valid under the rules set up by the International Commission of Zoological Nomenclature. Such names are still useful, however, in referring to commonly-encountered aberrations and seasonal forms, and Masters (i972) proposes rules pertaining to the use of such “infrasubspecific” names. In this book, aberrational names are enclosed within quote marks, but not underlined (as are valid scientific names).
Variation within butterflies and the causes of such variation are fascinating subjects that warrant much further work.
Butterfly Morphology
Morphology is the study of form and structure, and butterflies have some interesting structures worth mentioning.
The Proboscis
The structure through which liquid nourishment is taken up by the adult is a specialized ''mouth” known as the proboscis. The proboscis is basically a hollow tube and nectar is taken up by capillary action. The proboscis is not easily seen unless the butterfly is actively feeding, for it can be coiled into a compact and inconspicuous form when not in use.
Butterflies sense the presence of food through sensory structures located on the tarsi (the last segments of the legs).
The Wings
The beautiful wing patterns are derived from “scales”, which form a shingle-like cover on both the dorsal (top) and ventral (under) sides of the wings. The scales (and pattern) are easily rubbed off; hence, collectors try not to touch the wings when handling specimens. Scales come in many shapes and sizes and some excellent close-up color pictures of butterfly scales maybe seen in Brewer (1977) and Emsley (1975). Scale color is usually due to presence or absence of certain pigments; iridescent colors, however, are due to the breaking-up of light by specialized, hollow, vein-like structures (known as lamellae) found on the scales; pigments are not involved. The end result is much like the iridescent colors in a soap bubble or a thin oil film exposed to light. Butterflies may also exhibit invisible color patterns on the wings (Scott, 1973a). These ultraviolet reflective patterns, while invisible to humans, are visible to the butterflies and evidently play a role in species and/or mate recognition.
On many male butterflies, some scales are specialized as scent-producing organs; these are used (or presumably used) in mate attraction. The sex patches on the dorsal forewings of many male hairstreak butterflies (family Lycaenidae), the stigmas on the forewings of many male skippers (family Hesperiidae), and the sex patches on the hind wings of the male Monarch (Danaus plexippus are examples.
Sound Production
Do butterflies make sound? Surprisingly, some do. Frings and Frings (1960) record at least 40 families of butterflies and moths that produce sound during one or more stages of their lives. A few adult butterflies, such as the Giant Skipper (Megathymus sp.) produce sounds (Scott, 1973), as do the pupae of a large number of butterflies in the families Lycaenidae and Riodinidae (Downey, 1966; 1973). Even the pupa of the common Monarch Butterfly (Danaus plexippus) has been heard to make an audible click (Downey, 1966). It is probable that sound production is a protective measure used by pupae to startle potential predators. For those butterfly species closely associated with ants, the sound may also serve as an auditory signal for ants. Those morphological structures which produce the sounds have been identified in pupae of species of the family Lycaenidae, and are illustrated via scanning electron micrographs by Downey (1973).
Butterfly Biology
In discussing the biological attributes of butterflies, both at the individual and at the population level, one thing is obvious. Regardless of what aspect of the butterfly's biology we are considering, generalization is simply not possible. One can find butterflies both in the arctic and in the tropics, in the deserts and in the forest, at high elevations and low elevations, and in the winter as well as the summer. The diversity among butterfly “life-styles” is very great indeed, .y and logically so: Butterflies have adapted to a multitude of environmental conditions. These adaptations explain the great success of butterflies in having colonized most of the earth's landmass. Adaptations have taken many forms, some of which will be described in the following pages.
Life Cycle
All butterflies go through four stages in their life history; this development is commonly referred to as metamorphosis. The immature stages (egg, larva, pupa) are elaborated on below:
The Egg
The butterfly egg is a thick-shelled structure in which the embryo develops, and is rarely over one or two millimeters in diameter. Although small, butterfly eggs are in every other respect remarkably diverse. Some are rounded in shape, others turban-shaped or cigar-shaped. Some have a smooth surface, while others are variously sculptured with ridges, pits, and/or hollows. Color and luster varies tremendously. Colors of eggs of some Orange County species illustrate this: “creamy-white” (Lycaena gorgon), “whitish” (Colias eurytheme), “lemon yellow” (Papilio zelicaon), “deep orange” (Anthocaris sara), “pale green” (Everes amyntula), “rich jade green” (Incisalia augustinus iroides, “delicate pink” (Apodemia mormo) (all from Emmel and Emmel, 1973). Not only are the eggs of different species often of different color, but the eggs of a particular species may undergo a great color change. The egg of a duskywing skipper (Erynnis funeralis), for example, is white when laid and gradually changes color from green to orange, and finally to a deep brown. The egg of the Chalcedon Checkerspot (Euphydryas chalcedona) is first yellow, changing to red and finally to black just prior to hatching (Emmel and Emmel, 1973).
The eggs may hatch in a matter of days after being laid or depending on the species, may not hatch for eight or nine months. In the latter case., the eggs are in diapause which is simply a cessation of growth. Diapause in butterflies and other organisms is an adaptive response to unfavorable environmental conditions, such as cold temperatures, lack of larval food plant, dry summer months, etc. What better way to survive such environmental extremes than to remain dormant, emerging when conditions once again become suitable? Diapause in the butterfly conceivably may be “broken” or terminated in one of several ways; this varies with the species. Exposing the diapausing stage to cold temperatures (simulating winter) and then removing it from the cold may be sufficient to break diapause in some species. In other species, it may be necessary to expose the dormant stage to a specific photoperiod. Days are short in the winter and long in the summer, and many insects utilize this phenomenon to their advantage. Thus, by utilizing photoperiod, the butterfly can essentially differentiate between those seasons favorable for development and those that are not. The dormant period is terminated when it has been exposed to the photoperiod immediately preceding favorable conditions.
Although the egg stage is a hardy one, it is not invulnerable. Many butterfly species have egg “parasites”, organisms that feed within the egg. Many minute wasp species (of the family Trichogrammatidae) are known to be butterfly egg parasites and these tiny insects lay their eggs within the butterfly egg. The wasp larva hatches and proceeds to feed. Completing development inside the egg, it molts into a pupa, finally emerging as an adult wasp. Some wasp parasites can develop only in the egg of one species; others are not so particular. The study of parasites is a fascinating one; unfortunately, little is known about butterfly parasites.
The Larva
It would appear from observation that the “purpose” of the butterfly larva is to feed. Indeed, it is a rare sight when one sees a caterpillar that is NOT voraciously chewing away at the larval food plant. As the butterfly larva eats, it soon faces a dilemma. It inevitably must grow; yet, like larvae of all insects, the exoskeleton is rather inflexible - it cannot expand to accommodate this growth. The problem is solved by shedding the exoskeleton at intervals. This process is known as ''molting”. The new cuticle (the outer covering of the insect) is at first rather flexible and accommodates the larva. It then rapidly becomes the normal protective covering characteristic of all insects. The larva sometimes will eat the old “skin” at the time of molting. The number of molts during larval life varies with the species, and occasionally varies in individuals of the same species. In the latter case, the number of molts may be dependent upon the type of environment to which the caterpillar is exposed.
The Pupa
When the larva is full grown, it molts into the third stage of its life cycle, known as the pupa or chrysalis. The pupa is generally a stationary stage which does not feed. Some pupae are totally motionless; others make rapid jerking motions when disturbed, a function that may discourage predation. Some lepidopteran larvae (notably the moths) spin a silken structure known as the cocoon, within which they pupate. A simple silken thread “girdle”, spun around the stationary larva just prior to pupation, suffices for many butterflies; the “girdle” holds the pupa in place. During the pupal stage, tremendous changes take place, as the new adult exoskeleton is formed, and internal changes occur.
Flight Period, Number of Broods, and Diapause
Although all butterflies have egg, larval, pupal, and adult stages, the number of complete cycles or generations which occur in one year is remarkably variable, as is the time of year when each stage may be found. The greater portion of the year is spent in the egg stage in some species; for others, the larval, pupal, or adult stage is predominant. Knowing when each stage occurs is obviously invaluable in locating immature stages of any species; unfortunately, such information is not always published (although many individuals acquire such knowledge through experience). Some butterflies have only one generation per year; others are continuously brooded and have three or more generations per year. Several Orange County butterfly examples are given here to show the great diversity that can occur in a relatively small area.
The ANISE SWALLOWTAIL (Papilio zelicaon. Depending upon the elevation, this butterfly may either be multivoltine (i.e., multiple generations per year) or univoltine (one generation per year). When overwintering occurs, it takes place in the pupal stage. It is said that under unfavorable conditions, the dormant pupae (which are attached to the food plant) can remain in diapause for as long as seven years. Documented dormancies of several years are rather common.
The IMPORTED CABBAGEWORM BUTTERFLY (Pieris rapae. Not only is this butterfly multiple brooded, but generations overlap considerably; thus, one is apt to see all life history stages of this species at any time of the year. There is probably no diapause in southern California, i.e. the generations are continuous.
COMSTOCK'S FRITILLARY (Speyeria callippe comstocki. This species is univoltine, with adults flying in early summer. The eggs hatch soon after being laid. The emerging larvae, however, often find no food when they hatch, since the violet food plant has usually dried up by summer. Thus, the tiny fragile caterpillars overwinter in the ground until the following spring. When the 9 -10 month-old dormancy is finally broken, the larvae commence feeding on the new violet growth. The larvae grow, pupate, and soon emerge as adults, to begin another generation. In some fritillary species (genus Speyeria, the female will not lay eggs for a month or more after mating. Hormonal levels in the female change with time and affect the production of eggs.
RED ADMIRAL (Vanessa atalanta rubria. This species completes several generations during the warm months of the year. The overwintering stage is that of the adult, which roosts out of sight during the winter months. On warm winter days, however, the adults may fly about, only to disappear when temperatures again drop.
LORQUINIS ADMIRAL (Limenitis lorquini. Adults are found during the spring and again during the late summer and early fall, indicating two broods per year (i.e. bivoltine). The half-grown caterpillars resulting from the second brood roll up a leaf, holding it in place with “silk” produced by glands in the head. This shelter, known as a hibernaculum is where the caterpillars diapause during the winter months. The progeny of the first brood, however, do not diapause.
GREAT COPPER (Lycaena xanthoides). Unlike all of the previously mentioned species, this butterfly overwinters in the egg stage. Again, there is only one brood per year, adults flying for about one month in early summer.
SONORA BLUE (Philotes sonorensis). The adults of this univoltine butterfly fly for only a few weeks during the early spring. Unlike those species previously mentioned, it is the pupal stage that overwinters. These pupae may be found in the debris near the base of the larval foodplant.
It should now be obvious that a variety of strategies can be used for overwintering - any life history stage can overwinter, and diapause may occur in either the egg, larval, or pupal stage. In addition, there is great variation when adults fly, and whether they fly in one or in a series of broods. All this may appear rather obvious and simple, but there has been little comparative work to date to try to explain why, at a given locations, some butterfly species fly in one brood, while others fly in two or more. The explanation is often associated with the larval food plant. Perennial (those living more than one year) larval food plants may only be suitable when the new once-a-year growth appears. Butterflies utilizing such foodplants will probably have only one brood per year, the caterpillars being present during the period of new plant growth. Likewise, butterflies utilizing short-lived annual plant species cannot be multiple brooded unless different foodplant species are utilized by different generations during the year. Changes in the chemical content of perennial larval foodplants may prevent a butterfly from utilizing them as a suitable foodplant for more than a short period of time each year (Feeny, 1970). Other nutritive changes in a larval foodplant that which is available year-round may also prevent year-round utilization by butterfly larvae (Slansky, 1974).
The availability of adult nectar sources could influence the number of broods, particularly for those butterflies that are rather specific flower visitors.
Some generalization can be made concerning the number of broods in different localities (although there are many exceptions to these statements). Butterflies are almost always univoltine (one brood) at high elevations (correlated with the very short growing season of montane foodplants) although the same species might be multiple brooded at lowland locations. Likewise, the further one travels from the equator, the colder are the winters; butterflies and other insects living in more variable climates are more apt to have the ability to undergo diapause during the unfavorable period. Shapiro (1974) has examined winter diapause strategies of butterflies in the Sacramento Valley of California. Winters are mild enough there that butterfly larvae could continue development through the winter. Yet the pupae of the Imported Cabbageworm Butterfly (Pieris rapae) resulting from eggs laid in November overwinter until February or March. Why should these pupae diapause, when conditions are not harsh enough to prevent larval development? Why isn't the butterfly continuously brooded, adults being present year-round? Shapiro thinks that diapause serves as a timing mechanism correlating the spring emergence of adults with the onset of favorable adult breeding weather, i.e., sunny, warm days. In the Sacramento Valley, overcast or foggy days are common during winter months, and such days are unfavorable for butterfly flight (and hence, courtship, mating, and egg-laying). Thus, although Imported Cabbageworm Butterfly larvae can develop at any time of year in the Sacramento Valley, adult mating cannot occur successfully during the winter months. Hence, this unfavorable adult period is spent as an overwintering pupa.
The length of the flight period for a single-brooded butterfly species may also vary greatly, depending upon where the populations are located. Langston (1974) investigated flight periods of coastal and inland populations for a large number of primarily central Californian butterflies. He found that flight periods were longer for the coastal populations. This difference, as Langston speculates, is probably due to the staggered development of some coastal food plants (compared with inland plant populations). The greater life span of many annual food plants along the coast, compared with inland, may also explain this observation. This influences the length of time in which butterfly larvae can utilize the food plant. All this, in turn, is due to the differing climate between coastal and inland locations; climate might influence butterfly development directly as well.
Life span
Little is known concerning the length of a butterfly adult's life. A general rule is, the larger the butterfly, the longer it lives. A small butterfly in the family Lycaenidae may have an average life span of but a few days, some individuals living perhaps as long as a week (see e. g, Scott and Opler, 1975; Scott, 1971). Some butterflies in the family Nymphalidae may live several weeks (Smithers, 1973). The common Imported Cabbageworm Butterfly (Pieris rapae) may live up to one month. The Monarch Butterfly is known to be able to live six months (Smithers, 1973), and some individuals almost certainly live even longer. Scott (1973) correlated temporarily increased mortality in two species to hot weather; thus, local weather conditions may greatly affect lifespan.
Mate Location and Mating
Behavior is of immense importance in butterfly mating. Initially, one sex must locate the other; this may be accomplished through perching (males perch on an object and investigate any approaching object, in the “hope” that it will be a receptive female), or patrolling (males fly and investigate objects in the habitat in an effort to find receptive females). Either of these strategies may work in conjunction with pheromones (a chemical “scent”, often produced by the female, which aids males in locating females; in butterflies, these pheromones appear to function only as close-range attractants; Scott, 1974). Although the presence of patrolling or perching males may appear to indicate territorial behavior, butterflies do not appear to be territorial in the same way as vertebrates are, i.e. they do not actually defend a spot against intruding butterflies.
In those butterflies studied, perching species generally mate only in limited areas of habitat and during certain times of day, whereas patrolling species are more general in regard to location and time of day of mating (Scott, 1975). Also, perching appears to be more prevalent in those species with one or two broods per year. Some species exhibit both perching and patrolling behavior, and the extent to which each occurs may be dependent on time of day and perhaps the type of habitat present (e.g. the number of sites for perching which is available).
Hilltopping is a behavioral attribute found in a great many butterfly species. Hilltopping is simply the congregation of butterflies on the summits of mountains, ridges, and hills. A review of the phenomenon by Shields (1967) has resulted in plausible theories to explain this behavior. Males hilltop with much greater frequency than females. In addition, females that are found hilltopping are frequently virgin, whereas mated females are generally found elsewhere. Thus, hilltopping apparently functions as a mechanism to bring unmated females and males together; this is done through the concentration of both sexes in relatively high density on hill and mountain tops. Further investigation of hilltopping behavior in butterflies and other insects is warranted and Shields (!967) suggests possible directions in which future work might be concentrated.
Thus far, we have talked only about the initial location of a butterfly mate. Once the mate is located, mating does not necessarily follow automatically; certain behavioral prerequisites must first be satisfied. This behavior (leading to mating) is termed courtship behavior. Mating and courtship behavior may change with age (Scott, 1972). Some butterflies can mate on the first day of adult life (this is generally truer for females, although little data is available for males.) Courtship behavior is usually exhibited by males throughout their lives, but the type of the response given by the female varies, dependent on age (Scott, 1972) and when and if the female has mated.
Vision appears to play an important role in both mate location and courtship behavior. Movement, size, and general color (including ultraviolet reflectance patterns, as mentioned earlier) also appear to be important criteria for many butterflies. Magnus (1961) found that an important visual factor, in addition to the mere sight of the attractive color pattern, was the exposure and disappearance of that color (caused by the opening and closing of the wings of the female). Thus, the male sees a repetitive flash of color when the female is in flight. Using artificial butterfly dummies, Magnus found that males responded to flash frequencies far greater than what one would see in a live butterfly. In fact, males were maximally stimulated by these “supernormal” flash frequencies.
The physical movements involved in courtship behavior are hard to describe in general terms, since each species is unique. Females often exhibit a certain behavior for rejecting males, different from that displayed when accepting a male. This rejection behavior may consist of or include a rapid fluttering of wings, the spreading of wings, the closing of wings, etc. (Scott, 1972). If the male is not initially rejected, the female may land after a male-female encounter; following this the male usually lands beside or behind the female, but may occasionally hover above the female for a few seconds before landing. The male then often performs complex maneuvers, using the legs, wings, antennae, etc. Interested readers are urged to consult Scott (1972) for additional details.
Once mated, the copulating pair remains rather quiet. The duration of copulation appears to be reasonably constant in many species, although it may vary, dependent upon temperature and the prior mating experience of the male (Scott, 1972). To get an idea of the diversity involved, examples of mating durations of some species (from Scott, 1972), which are Orange County residents, are as follows:
Anise Swallowtail (Papilio zelicaon) --36 minutes up to 30 hours if the male has recently mated; Imported Cabbageworm Butterfly (Pieris rapae) --80 minutes; Common White (Pieris protodice) --”frequently overnight”; orange-tip (Anthocaris spp.) --25 minutes to 4 hours, rarely to next morning; Queen Butterfly (Danaus gilippus) --100 minutes to 12 hours, usually several hours.
During copulation, the male deposits sperm in the female via a “sperm package” known as the spermatophore, which functions to protect the sperm from desiccation. The female stores the spermatophores in receptacles known as spermathecae (sing. spermatheca), and eggs are fertilized one by one, just before deposition. One can often determine the number of times a female has mated by killing the animal, dissecting the abdomen, and counting the number of spermatophores present. In members of the genus Lycaena (the “coppers” of the family Lycaenidae), however, the spermatophores are rapidly broken down by the female, which makes it hard to determine the number of matings.
The number of matings for both sexes has been investigated in many butterflies. The number of times a male can mate varies among different species. Males of the Imported Cabbageworm (Pieris rapae and the Buckeye (Precis lavinia coenia) can mate at least twice, whereas the Alfalfa Caterpillar Butterfly male (Colias eurytheme) can mate at least four times on successive days, and the Common White male (Pieris protodice) can mate at least 13 times (Scott, 1972). In contrast to the male, the number of matings per female, judging from present data, is not highly variable. Few species are known where the female regularly mates more than once or twice. The males of some butterflies inhibit further mating by the female by inserting a “plug” (sphragis) into the female genital opening immediately after mating. Such plugs are found in the Edith Checkerspot (Euphydryas editha) (Labine, 1964), and also butterflies of the genus Parnassius (family Papilionidae).
Mating pairs of butterflies often take flight (remaining in copulation) when disturbed. Numerous observations on many species have shown that usually only one sex flies when the copulating pair is disturbed. The male may fly when copulating pairs of one species are disturbed, whereas the female mayfly in another species; related species often have similar carrying-pair behavior (Shields and Emmel, 1973).
Mating, of course, generally occurs between males and females of the same species. However, as was mentioned earlier, hybrid individuals may result from that rare successful mating between two closely species. Unsuccessful matings between less closely-related species are also known, and attempted matings between individuals of species representing different butterfly families have even been recorded, such as between a nymphalid and lycaenid (Johnson, 1974), or a nymphalid and a pierid (Shapiro, 1972). Considering the fact that such unrelated butterflies probably have completely different courtship and mating behaviors, it is amazing that butterflies that are distantly related would show any interest in each other at all.
Laying Eggs
After the female has mated, she is ready to lay eggs (a process known as oviposition). There is little information concerning the time between the termination of mating and the initiation of oviposition; however, I once observed a female of the Bright Blue Copper Butterfly (Lycaena heteronea clara), which commenced laying eggs a few minutes after mating was terminated. The female butterfly is often very particular about laying eggs. First, she has to locate the larval foodplant. Vision certainly plays a role in this; olfaction is also probably important, particularly at close range (see “Other Remarks” under Papilio zelicaon, page 72). Once the foodplant is located, the female may brush the tip of her abdomen across the foodplant leaf before laying an egg; thus, proper tactile stimulation may also be necessary,
Many butterflies lay their eggs on the leaves of the food plant (e.g. the Imported Cabbageworm Butterfly, Pieris rapae). Others, primarily those whose larval foodplants are woody, lay eggs on the stems (often in cracks in the bark, twig junctions, etc). Examples of such butterflies that occur in Orange County are the Sylvan Hairstreak (Satyrium sylvinus and the Tailed Copper (Lycaena arota). Still other butterflies lay their eggs in flower buds (e.g. the diminutive Bernardino Blue, Shijimiaeoides battoides bernardino). Finally, to complete the picture of what is obviously very diverse behavior, some butterflies do not lay eggs on the living foodplant at all, but rather on the dead leaves of the foodplant (e.g. the fritillary butterflies of the genus Speyeria) or on other twigs, dead leaves, etc. that may not even be on the foodplant (but that are near the foodplant) (e.g. the Melissa Blue, Plebejus melissa inyoensis). Many butterflies of the family Satyridae do not attach the eggs to a substrate at all, but merely “flick” them in the general direction of the foodplant.
One can sometimes force immature insects to feed on plants that are not utilized in nature (but that may still be nutritionally suitable). If the adult females that develop from these immatures are allowed a choice between the plants on which they were reared and the plant that is normally utilized by the species, they will often pick the former. Hopkin's Host Selection Principle describes this behavior of a female selecting the same host upon which she was raised over other hosts (including those which might be normally utilized in nature); the details of this behavior
are still not well known, but it could help us explain why some species consistently utilize several foodplants in a given area. In other words, when two or three foodplants are utilized within a small area, we could attribute this to 1) females which lay their eggs on all foodplants available, or 2) two or three “types” of females, each of which chooses only the foodplant upon which she was raised to lay her eggs (as stated by Hopkin's Host Selection Principle). The different female “types” would choose different foodplant species.
Nectaring
Most butterflies utilize the nectar of flowers for food. A few prefer to feed on sap exudates from trees, and many occasionally or frequently “puddle”. An unusual butterfly food was observed in 1975, when I encountered individuals of the Great Copper (Lycaena xanthoides) “nectaring” on the sweet “honeydew” secreted by a huge population of aphid insects on a grove of willow trees in the Tehachapi Mountains of Kern County. Butterflies derive carbohydrates, and also some amino acids (the “building blocks” of proteins) from flower nectar. Not all flowers produce nectar and those which do not (e.g. most lupines; H. G. Baker, personal communication) will not have butterfly visitors. However, even nectar-producing flowers may not be attractive to butterflies. In order for a flower species to be visited (and potentially pollinated) by butterflies, the butterflies must (1) be able to see it and be attracted to its color, (2) be able to alight on it, (3) be able to get at the nectar which is present, and (4) be amply rewarded by the nectar (e.g. in the amount of its sugar concentration) to result in subsequent visits. Some flowers have evolved so that they are attractive primarily to honeybees; such flowers are thus usually pollinated by these insects. Likewise, there are plants in temperate and/or tropical regions that have evolved flowers that are highly attractive to either beetles, flies, butterflies, moths, birds, or even bats. By closely examining a flower, one can often deduce what insect or other animal is the most frequent pollinator. For example, a flower which produces a large amount of nectar over a short period of time is likely to be pollinated by an animal which requires a great deal of energy - probably a hummingbird. Yet, if flowers pollinated by insects produced huge amounts of n e c t a r, the insects would probably become satiated after visiting just one or two flowers, and would not need to visit additional blossoms. This would reduce cross-pollination in that plant species, possibly resulting in fewer seeds being produced; of course, this would not be in the “best interests” of the plant.
It is difficult to characterize “butterfly flowers”, although some generalities emerge. Small butterflies generally visit flowers that grow in clusters; this makes a convenient perch for the butterflies (although the much larger swallowtail butterflies, for example, often hover while nectaring). Butterfly flowers tend to be blue or yellow in color, sometimes orange or white. Different butterflies might prefer differently colored flowers. Additionally, a flower that might be often utilized as a nectar source in one region may be totally ignored in another, for a variety of reasons. Considerable study is needed to determine how specific different butterflies are in visiting flowers, and the reasons behind such specialization. The first step in such a study is to determine which flowers are present at a specific site and the times during which those flowers bloom. Then, one determines which blossoms are visited by butterflies and which are not. The final step (which actually may involve many steps) is to determine the reasons for the butterflies' preferences. Are the flowers which are most frequently visited also the most common at the site? Are those flowers that are often visited by butterflies of a specific color? a specific shape or size? Are they found at a specific height? Do some butterflies ignore flowers that other butterfly species prefer? Such questions are not always easy to answer, and what appears to be the obvious reason for preferential flower visiting may not be a factor at all. To illustrate, on one occasion while collecting in Frazier Park (Kern County), I noticed that a small blue-flowering plant (Eriastrum densifolium var. elongatum) was visited avidly by several large swallowtail butterfly species (Papilio rutulus, P. eurymedon, and P. multicaudatus), the Imported Cabbageworm (Pieris rapae) and the Chalcedon Checkerspot (Euphydryas chalcedona), yet was completely ignored by all of the small butterflies (of the family Lycaenidae) found at the site. I first theorized that flower color was probably responsible, since the small butterflies were avidly visiting the white blossoms of Wild Buckwheat (Eriogonum fasciculatum). Other factors that I thought might be involved in determining butterfly preference were the amount of nectar produced by both flower species, or the nectar composition (e.g. sugar concentration). Upon closer inspection of the flowers and the butterflies nectaring on them, however, the real reason became obvious. The blue flowers consisted of a relatively long flower “tube” (the corolla). Only organisms with long mouthparts would be able to reach the nectar at the base of the flower tube. Hence, the larger butterflies (with their long probosces) were able to reach the nectar, the medium-sized butterflies, such as the Imported Cabbageworm were just barely able to reach it (they had to stick their heads deep into the flower), and the small butterflies (with their very short probosces) were not able to reach the nectar at all. On the other hand, the small butterflies could easily reach the nectar produced by the tiny Wild Buckwheat blossoms. This is not to say that the nectar of the blue flowers would have been nutritionally suitable for the small butterflies, or that the color was attractive. Even if these characteristics had been attractive to the small butterflies, however, the flower morphology still would stand in the way of their obtaining nectar.
Puddling
Several recent authors (Arms et al., 1974; Downes, 1973) have done much to explain the phenomenon of “puddling” in butterflies and moths. “Puddling” refers to the attraction of large numbers of lepidopteran adults to the margins of puddles and streams (and often to animal feces or carrion) to “feed”. It was originally thought that puddling was related to water requirements, i.e., thirsty butterflies “puddled”. However, puddling could be observed even when nearby water was plentiful and available; it also commonly occurs on dry substrates, e. g. at dried-up pools of water or on dry dung or carrion (Downes, 1973). Experiments conducted by Arms et al. on the Eastern Tiger Swallowtail (Papilio glaucus) show that these butterflies probably puddle to acquire essential sodium. Amino acids are also acquired through puddling. These findings may explain puddling in most other butterflies, making the behavior of carrion and dung-feeding butterflies easier to understand.
Roosting and Basking
At night, where are the butterflies? Thus far, few lepidopterists have bothered to find out, probably because many believe butterflies pick roosting locations at random. Those butterflies that are closely associated with their larval foodplant (many members of the family Lycaenidae), however, may preferentially rest on that foodplant. Also, some butterflies apparently prefer to rest in shrubs, no matter what growth form the foodplant is. Others may roost in crevices of various sorts.
“Basking” is a phenomenon that can be observed in most butterflies; the function of this behavior is to regulate body temperature. On cool days, in the early morning and late afternoon, one often sees butterflies perching with open wings. The wings absorb heat, which is then transferred
to the body. In contrast, on very hot days (particularly true for those butterflies which commonly “perch”) one often sees perching butterflies with completely folded wings, so as to absorb as little heat through the wings as possible. See Clench (1966, 1975) for further details on thermoregulation in butterflies.
Natural Enemies
Like all organisms (with the possible exception of modern man) butterflies are preyed upon by a variety of other organisms. These organisms can be grouped into three categories: predators parasites, and pathogens. Included in the predator category are birds, spiders and insects (such as dragonflies, robber flies of the family Asilidae; also assassin and ambush bugs of the families Reduviidae and Phymatidae, respectively). Occasionally, in the course of collecting butterflies, one comes across specimens with a v-shaped tear or mark on the wings (usually the hind wings). This damage often results from a bird beak; this might suggest either an unsuccessful attack (in which the butterfly escaped) or the voluntary release of the butterfly by the bird, because the butterfly was distasteful. Such butterflies escaped bird predation. However, one must remember that for the few that escape, many do not. Shapiro (1974) analyzed the frequency of bird beak marks in populations of several butterfly species and found seasonal changes in the frequency of attacks.
We mentioned parasites earlier in this chapter, in the context of butterfly development. Both flies (those in the family Tachinidae) and wasps (e.g. in the families Ichneumonidae, Braconidae, and Trichogrammatidae) parasitize one or more of the immature stages of many butterfly species (i.e. egg, larva, and pupa). Some parasites are quite specific, attacking only one or a few related butterfly species; others are rather nonspecific, attacking a great variety of butterfly species in one or more families. Wasp species that parasitize larvae lay their eggs either on or in the butterfly larva. Many tachinid flies, on the other hand, lay their “microtype” eggs on foliage where they are subsequently ingested by the butterfly caterpillar. Once inside, the eggs hatch. The number of parasite eggs laid in the butterfly host may vary. From one to as many as several hundred individual parasites may emerge from just one host. Often, multiple-emerging parasites are polyembryonic species, i.e., only a few eggs are laid, but subsequently each gives rise to many individuals (rather than the normal situation in which only one insect emerges from one egg). Parasitism generally does not appear to exert much influence over butterfly populations, although few studies have concentrated on the extent of parasitism in a population. Those species that do have a high parasitism rate are generally those which occur in dense populations. For example, Michelbacher and Smith (1943) found parasitism of Alfalfa Caterpillar Butterfly (Colias eurytheme) larvae by a wasp (family Braconidae, genus Apanteles) as high as 100%.
Diseases, particularly viruses, may take a heavy toll of butterfly larvae, although pathogens generally have not been well studied. Disease is generally prevalent only when larval butterfly populations occur in high density. Many bacterial and viral diseases are not at all specific, attacking moth and butterfly larvae of all kinds.
Avoiding Predation
There are numerous ways by which a butterfly can minimize the chances of being eaten. Eggs are often cryptically colored to blend in with their surroundings; they are also often laid in places (e. g. the underside of the leaf or in bark crevices) where they are not easily visible. Many butterfly larvae are likewise cryptically colored. Some larvae possess tubercles or spine-like projections on the body, which may serve a cryptic function or as a feeding deterrent.
Larvae of swallowtail butterflies (family Papilionidae) have rather unique structures, known as osmeteria, to ward off potential enemies. These are soft, retractable orange structures (resembling “horns” when protruded), which are normally kept in the retracted condition. When a larva of the Anise Swallowtail (Papilio zelicaon is disturbed, however, the osmeteria immediately appear. Not only could this sudden flash of color discourage would-be predators, but the protuberances emit a strange odor which also might discourage predation. The mere appearance of sharp-looking protuberances may also help minimize predation.
Some larvae, instead of blending in with the surrounding environment, have bright and/or contrasting colors, which readily stand out and attract attention. Such larvae are invariably distasteful, and their warning coloration (known as aposematic coloration) makes them easily recognizable to potential and past predators. A good example of this is the white with yellow and black transverse banded larvae of the Monarch Butterfly (Danaus plexippus). Adults of the Monarch Butterfly are also rather strikingly colored, and well remembered by any bird that has had the misfortune to select a Monarch for dinner. Monarchs contain poisons (cardiac glycosides), which are derived from the foodplant, milkweed. In fact, monarchs are so well protected by their distastefulness that one rather tasty butterfly, the Viceroy (Limenitis archippus) has, over time, evolved to closely resemble the Monarch in shape, wing pattern, and color. Thus, birds that have learned to avoid the Monarch will also mistakenly avoid the edible Viceroy Butterfly. The evolution of an edible “mimic” to resemble a less palatable “model” is known as Batesian mimicry. In Orange County (and most of California) two butterflies, the California Sister (Adelpha bredowii californica) and Lorquin's Admiral (Limenitis lorquini--closely related to the Viceroy butterfly) are often found flying in the same general habitats. Both are extremely similar in pattern and coloration, and may represent another example of Batesian mimicry.
Like many butterfly caterpillars, many butterfly adults are cryptically colored, particularly on the ventral wing surfaces. A good example is the Mourning cloak Butterfly (Nymphalis antiopa). The ventral wing surfaces of this species resemble a piece of bark, and it is not hard to see why this butterfly is often very difficult to find, once it lands on a tree branch. The greenish undersides of the Bramble Hairstreak (Callophrys dumetorum) may likewise fool a potential predator into mistaking the butterfly for just another green leaf on a chaparral shrub.
Hairstreak butterflies (family Lycaenidae) employ a rather novel means of avoiding, or at least, minimizing the effects of a predator. The tiny thread-like “tails” on the hind wings could easily be mistaken by a predator for antennae; likewise, dark spots on the ventral surface of the hind wings next to the “tails” might be mistaken for eyes. These butterflies also are often seen engaging in moving their hind wings back and forth against each other while at rest. Wickler (1968) theorizes that this may be a behavioral protection mechanism to draw attention to the false “eye” and “antennae”. If a predator mistakes the false head on the wings for the real one, the butterfly may escape with only a portion of the hind wings missing (a distinct advantage over a butterfly whose only obvious head is the real one).
Many butterfly and moth species possess scale patterns (particularly on the hind wings) that resemble large eyes. Known as eyespots, these patterns may also minimize predation. If the butterfly or moth possessing the eyespots otherwise blends in with the surrounding environment, a predator is likely is assume that the “eyes” belong to a much larger animal (on account of their size) and may thus avoid the insect. This concept is combined with the element of surprise in some insects, such as the Io Moth (Automeris io). The large eyespots on the hind wings of this insect are generally not visible when the moth is at rest, being covered by the somewhat cryptically colored forewings. When disturbed, however, the Io quickly moves the forewings up, exposing the eyespots of the hind wing -- it is thought that this alone is sufficient to scare away the intruder.
Butterflies and Ants
Ants often can be seen tending aphids (plant-sucking insect pests), “milking” them of a sweet substance and at the same time protecting them from natural enemies. Similarly, larvae of some butterflies are also “tended” by ants. This is true for butterflies of the family Lycaenidae (comprising the “coppers”, “blues”, and “hairstreaks”). This association with ants is known as myrmecophily, which means “ant-love”. Most lycaenid butterfly larvae studied possess a honey gland on the tenth body segment, which exudes a fluid utilized as food by the tending ants (Downey, 1961). Larvae of several butterfly species occurring in Orange County have been elsewhere recorded in association with ants; Plebejus Acmon, Plebejus icarioides, and Glaucopsyche lygdamus, all of which are members of the butterfly family Lycaenidae.
Downey (1965) also observed thrips (of the insect Order Thysanoptera) utilizing the sweet larval secretions of lycaenid pupae and cites additional papers on myrmecophily in lycaenid larvae.
Ants appear to protect myrmecophilous butterfly larvae and pupae from natural enemies and have even been known to transport the larvae to the ant nest for shelter, where the larvae may pupate (Downey, 1961).
Butterfly and Foodplant Interrelationships
The relationship between butterflies and their larval foodplants has already been considered in several contexts, e.g. the correlation of life history stage presence with foodplant quality, or the laying of eggs by the female on the plant. Usually when the foodplant is absent from a region, the butterfly is also absent, although migrating species may travel into very unsuitable breeding habitats. Is it also true that wherever the larval foodplant occurs, the butterfly will also occur? Not necessarily. Before answering this question, however, one must know exactly what the foodplants include. Preciseness is a virtue in determining which plants are utilized as foodplants by a butterfly. One might surmise, for example, after watching an Icarioides Blue butterfly (Plebejus icarioides) lay an egg on the Bush Lupine (Lupinus excubitus) that it would probably also lay eggs on other closely-related lupine species growing in the immediate vicinity. Nothing could be further from the truth. The Icarioides Blue apparently oviposits on only one lupine species in any one area (regardless of how many other species are present), laying eggs generally on the most hairy species present (Downey, 1962). Yet, over its entire range this butterfly utilizes a large number of lupine species for foodplants. In contrast, some butterfly species utilize only one foodplant over their entire range. Examples of this include Wright's Metalmark (Calephelis wrighti), the Gray Hairstreak (Satyrium tetra), and the California Sister (Adelpha bredowii californica). Such butterflies are often as scarce or as common (or as restricted or as wide-ranging) as is their sole larval foodplant. At the other extreme, there are butterflies such as the Sara Orange-Tip (Anthocaris sara), and the Imported Cabbageworm Butterfly (Pieris rapae), which utilize a large number of species in one plant family (Cruciferae); also the Painted Lady (Cynthia cardui) and the Common Hairstreak (Strymon melinus), which utilize larval foodplants representing several plant families.
Getting back to our original question and given a butterfly that utilizes one foodplant species (to simplify), would we expect that butterfly to be found everywhere that the foodplant grows? Obviously, the amount of foodplant present at a given site is an important factor determining the presence or absence of a butterfly. For a small butterfly (which has small caterpillars) utilizing a tree as a foodplant, a few such plants might be sufficient to support a healthy colony. An example of this might be Boisduval’s Hairstreak (Habrodais grunus), whose foodplant is an oak. On the other hand, Wright's Euphydryas (Euphydryas editha wrighti), which utilizes a diminutive annual plant (Plantago erecta) as a foodplant, probably requires hundreds of individual plants to support the smallest viable colony.
Foodplant quality can fluctuate as a result of changing climatic conditions, and this may also affect butterfly populations. An exceptionally late snowstorm in Colorado in 1969 resulted in the documented extinction (Ehrlich, et al., 1972) of a population of the Silvery Blue (Glaucopsyche lygdamus) through the freezing and subsequent destruction of the floral parts of the foodplant (lupine) on which the female butterfly lays her eggs. Likewise the density of a secondary larval foodplant of the checkerspot butterfly (Euphydryas editha) was found to fluctuate from year-to-year, possibly due to changing climatic conditions, and this affected larval survival and hence, adult population size (Singer, 197Z).
Larval foodplant quantity although extremely important, is not the only factor determining a butterfly's presence or absence. Larval food plant quality may also affect the presence or absence of a butterfly (even at sites where the foodplant grows abundantly). For example, the Bernardino Blue Butterfly (Shijimiaeoides battoides bernardino) lays its eggs on flower heads of Wild Buckwheat (Eriogonum fasciculatum). The larvae of this small butterfly subsequently develop on the flower head. Buckwheat plants growing in areas with an ample water supply generally produce large flower heads; plants growing on steep, south-facing slopes and other dry areas often are desiccated in appearance and produce very small flower heads. The Bernardino Blue may be absent r occur in very low densities at sites where small foodplant flower heads are prevalent, since a lower percent of flower heads in such an area would be suitable for larval development.
Foodplant quality can also temporarily change as a result of prevailing climatic conditions. Fritillary butterfly (genus Speyeria populations often fluctuate noticeably from year to year. Drought years appear to induce high mortality and the lack of rain probably acts directly on the moisture-dependent violet foodplants. Rainfall also probably affects the quality of Plantago erecta the small annual foodplant of Wright' s Euphydryas (Euphydryas editha wrighti). In years with low rainfall, the plants are rather small and stunted; plants growing in depressions which collect water or which grow during years with ample rainfall tend to be much taller and hence would provide more food for a developing larva.
Another factor which can determine the suitability of an individual foodplant is its chemical make-up. Plant species that are extensively utilized for food by insects and other animals have often evolved structures to ward off intense predation. Defense strategies may take many forms; the plant may evolve spiny structures, for example. Plants may also evolve to produce or contain chemicals that are either distasteful or poisonous to potential herbivores (plant feeders). These defense strategies, while extremely effective at first, are rarely permanently protective. Usually an herbivore will evolve mechanisms to breach or utilize these plant defenses. Three strategies can be used. The herbivore can (1) excrete these toxic substances unchanged, (2) convert these substances into non-toxic or more easily excreted compounds, or (3) use these compounds in their own defense system (Dolinger, et al., 1973). A good example of the latter is the Monarch butterfly caterpillar, which feeds on milkweed (family Asclepiadaceae). Many milkweed species contain poisons known as cardiac glycosides. Monarch larvae are unaffected by these poisons and the compounds are incorporated into the caterpillar and subsequently, the adult. As we mentioned earlier, many adult Monarch butterflies are loaded with cardiac glycosides, which minimizes their chances of being eaten by birds. A bird making the mistake of eating a Monarch will soon become violently ill as a result of the cardiac glycosides and will subsequently avoid that butterfly.
Alkaloids are a very common class of plant defense compounds. Dolinger et al. (1973) studied the Silvery Blue (Glaucopsyche lygdamus) and its lupine foodplant in Colorado. It was found that wherever the butterfly was absent (due to factors other than foodplant presence), there were few alkaloid compounds present in the lupines growing at those sites; those alkaloids present also occurred in relatively small quantities. Contrastingly, at sites where the butterfly was present and abundant, and whose caterpillars exerted intense predation on the lupine foodplant, a wide variety of different alkaloid compounds were found in the plant. These results suggested that the plants may be evolving alkaloid variety in response to heavy predation by the butterfly larvae. These alkaloid compounds, in turn, might eventually result in decreased predation of the plant because of their toxic effects on the butterfly larvae.
Butterfly Movement
Dispersal, Migration
There is an enormous amount of variation in the distance traveled by a given butterfly adult during its lifetime. There is variation between species and variation between individuals of the same species. Migrating butterflies have been observed for well over one hundred years and innumerable notes and papers have been published on the phenomenon; yet, little is known concerning the factors responsible for initiating and controlling migration. A number of butterflies found in Orange County are migratory species in California and/or elsewhere and the Orange County records may often represent individuals that flew in from outside the county. Migratory or highly dispersive species for which we have Orange County records include the Monarch (Danaus plexippus), Painted Lady (Cynthia cardui), Sleepy Sulfur (Eurema nicippe), Cloudless Sulfur (Phoebis sennae marcellina), Snout Butterfly (Libytheana bachmanii larvata), and California Tortoiseshell (Nymphalis californica). The only one of these species with predictable yearly migrations is the Monarch. From September to November, one occasionally sees adults flying in a northward direction in Orange County; these adults are probably on their way to coastal overwintering sites in central California (particularly around Pacific Grove in Monterey County). Those butterfly species that migrate irregularly appear to do so when their populations reach a very high density.
What exactly is responsible for initiating migration or dispersal from an area? (Migration, unlike dispersal is a directed movement). What do migrating insects use to orient themselves? Currently, these questions have only been partially answered. Many things may be used in orientation. Wind direction, while so important in the undirected dispersal of many small insects (e.g. aphids) does not appear to play a major role in butterfly migration. Indeed, when winds become too strong, many migratory butterflies terminate flight rather than let the wind passively carry them. The sun could conceivably guide migrating butterflies although no examples have been documented. An interesting discussion of butterfly migration, which discusses these and other factors, is that of Shields (1974a); also Gilbert and Singer (1975). Factors accounting for short-distance dispersal from colonies in the Common White (Pieris protodice) were studied by Shapiro (1970). He found that the greater the population density, the more often male-female interactions would occur. These repeated interactions would cause females to move out of the high density population, which could result in some females emigrating to favorable but uncolonized habitats. It is not known how widespread this behavior is. In contrast to Shapiro, who found a high female:male ratio at the periphery of the colony, one always finds in at least some territorial butterflies a low peripheral female:male ratio; in other words, the peripheral butterflies are almost always males. In one butterfly that exhibits this (the Bright Blue Copper, Lycaena heteronea clara), the female, rather than leaving the area when disturbed excessively, usually lands and remains still until the male(s) leaves. Yet, the question still remains, how do these butterflies locate new sites for colonization? Dispersal from these colonies almost certainly occurs, although perhaps it occurs only when populations are unusually dense, as was the case with Pieris protodice.
Some general rules concerning dispersal and population size can be made. First, small butterflies tend to be less dispersive than larger butterflies; they seldom show migratory tendencies. Small butterflies tend to be very colonial, although some medium-sized butterflies (e.g. Wright’s Euphydryas, Euphydryas editha wrighti) also occur in well-defined colonies. The dispersal of individual butterflies from a population, as well a s the size of that population, is greatly influenced by the larval foodplant distribution. A female butterfly has basically two choices: it can choose to “play it safe” and remain where she has emerged, laying eggs on nearby foodplants, or she can take a chance, leave the site, and look for new, unexploited food resources. Of course, there may be a strong possibility that the butterfly choosing the latter alternative will fail to find the foodplant, and will die without laying eggs. The choice made is generally dependent on the distribution of the foodplant (also the permanency of the habitat). If the larval foodplant is not clumped in distribution, but instead is rather randomly or evenly distributed, the “risk” in leaving the site of emergence may not be a risk at all. Also, the amount of foodplant present at the site of emergence may not be sufficient to support the larvae of all the eggs laid by female butterflies emerging there. On the other hand, if the foodplant grows in large clumps, each clump widely separated from the next, there may be a very high probability that a butterfly leaving a clump of foodplants will not locate another foodplant clump. Which butterflies might utilize foodplants that are randomly distributed? Which might utilize foodplants that are clumped in distribution? Obviously, a butterfly that has large wings will usually be able to cover a greater distance than one with small wings. Thus, a small butterfly is better off utilizing a foodplant that is locally abundant (i.e. it doesn't have to leave the site of emergence to “chance being able to find new unexploited foodplant reserves”). On the other hand, a large butterfly may be able to cover a great distance, which increases its chance of finding an unexploited foodplant. Thus, large butterflies can “afford” to utilize a foodplant that is rather generally distributed over a greater area.
Movement Within A Colony and Artificial Displacement
A population may be simply defined as “a group of organisms of the same species living in a particular space” (Emmel., 1973). In the past, it has often been assumed that within one population, each individual has an equal chance of coming into contact with any other individual in that population; in other words, individuals in a population move randomly about. The possible fallacies of this generalization were shown by Ehrlich, in a study of the checkerspot butterfly Euphydryas editha (Ehrlich, 1961a). Although the population studied occupied a clearing in which there were no physical barriers preventing the butterflies from moving randomly about, the colony was actually found to consist of three “subpopulations”. Almost no movement between sub-populations was found to occur. Thus, upon closer inspection, a butterfly “colony” may actually be found to consist of more than one discrete population.
Movements of adult butterflies within a colony are often variable. For example, “territorial” males of the Bright Blue Copper (Lycaena heteronea clara) exhibit great variation in the extent of their movements within one colony (L. Orsak, unpublished observations). Some individuals were found to move from one end of the colony to the other in a short period of time (a few hours). Other individuals were found again and again at the same site in the colony for several days in a row.
A tendency to remain at or near the site of emergence is a wise strategy for colonial butterflies. Yet, what makes them stay? Perhaps butterflies use, as a measure of suitable habitat, the presence of other butterflies of the same species (Ehrlich et al., 1975). Hence, they tend to aggregate. On the other hand, a butterfly may tend to remain at the site of emergence because it uses features of the landscape to orient itself. This is suggested by Keller et al. (1966), who artificially displaced individuals of the Sonora Blue (Philotes sonorensis), discovering that a significant proportion of displaced individuals returned to the site of first capture. Unfortunately, these experiments have not been repeated for any other butterfly species, so we still do not know how widespread this behavior is.
Studying Butterfly Populations
How do lepidopterists determine the average life span of a butterfly? the movement of individuals in and between populations? the size of a population? All of these questions can be answered through a mark-release-recapture program, a study in which a lepidopterist goes out and marks all butterflies in a given population that can be captured. A felt-tip pen can be used in placing coded dots on the wings. The marked butterflies are then released. At a later time, there is another capture session. Those butterflies caught that were previously marked are so recorded and then released. Those butterflies not previously marked are marked at this time. This process is then repeated for any number of times the lepidopterist wishes (e.g. mark-release-recapture sessions could be held every other day for two weeks, etc.). In order to accurately estimate population size and average lifespan, it is imperative that certain conditions be met. The butterfly population chosen should be colonial, i.e. with little or no movement of individuals into or out of the population. 'The marked butterflies, when released, should be given enough time to mix into the population before another capture session is held. The markings on the butterfly should not be too conspicuous so that the marked butterflies are, for example, captured by birds more often than unmarked individuals. These conditions need not be met for a simple study of butterfly movement, but they are important if one wants to measure population size and birth and death rates.
The details of a mark-release -recapture program cannot be elaborated on here, but such a study can be both interesting and highly informative. For further details on the actual marking of the butterflies (with a coded dot system), see Ehrlich and Davidson (1960); also Brussard (1971). The specifics of gathering and analyzing the data is explained by Southwood (1964).
This has been a very brief sketch of the life and structure of butterflies. Each topic discussed could have easily been expanded into a lengthy paper, even a book in some cases; we have covered only the highlights. In addition, many interesting topics (e.g. competition, habitat selection, etc.) have not been discussed for lack of space. Yet, even with the obvious mass of accumulated information on butterfly biology and behavior, much remains to be discovered. Some suggestions for projects are scattered throughout this chapter, as well as throughout the book. Basic biological observations are often easy to make, and interesting as well. While each observation alone may merit little scientific interest, a series of observations can be highly valuable. Amateur lepidopterists, if properly guided, can make valuable contributions to our knowledge of butterflies; anyone interested in learning more about butterflies should be encouraged to initiate a study of some aspect of butterfly biology or behavior.
For an excellent detailed review of many of the topics discussed here (and others) see Gilbert and Singer (1975). A most interesting account of an intensive long-term study of the biology and behavior of one butterfly, Euphydryas editha, is that of Ehrlich et al.(1975). Clench (1975) is also an introduction to butterfly biology and structure, with many more details on butterfly structure than could be considered here.