Notonecta unifasciata

Hemiptera: Notonectidae

San Joaquin Marsh, Irvine, CA

Backswimmers are bugs about 10 mm long with large compound eyes. They swim upside-down, propelling themselves by rowing with their long hind legs trimmed with hair. They are also good fliers and have well-developed wings. They are widespread in the U.S.and can be found in slow-moving streams or ponds.

The most common backswimmers in and around the Los Angeles Basin are Notonecta unifasciata, Notonecta kirbyi, and Notonecta shooteri. Adult Notonecta unifasciata are white or dark green above and black underneath. Paler color variants are observed in the West.

Backswimmers use their forelegs to grasp prey (usually other aquatic insects or small aquatic vertebrates); then they use their piercing mouthparts to kill and suck fluids from the prey. If handled in a careless manner, a backswimmer can inflict a bite comparable to a bee’s sting; this characteristic earned it the alternative common names water wasp and water bee.

Backswimmers maintain an air supply by trapping air in pockets at the tip of the abdomen. This allows them to remain submerged (inactively) for up to six hours before they need to return to the surface to refill this air supply. Backswimmers can usually be found in a resting upside-down position at the surface, with abdomen making a connection with the air.

Males rub their front legs against their rostrum, to make a sound used in attracting a mate. After mating, females lay white eggs usually in a bunch of ten or less, either on or inserted into the leaves and stems of aquatic vegetation. The eggs hatch in a few weeks and the nymphs, like the adults, are vigorous predators.

Backswimmers can be attracted to swimming pool lights at night, and may become numerous enough to be considered pests; however, using orange pool lights or pool light traps and covers reduces this problem.

Sources consulted:

Arnett, Dr. Ross H., Jr. & Jacques, Dr. Richard L. (Eds.). (1981). Simon & Schuster’s Guide to Insects. New York, NY: Simon & Schuster, Inc.

Borror, Donald J. & White, Richard E. A Field Guide to Insects: America North of Mexico. New York: Houghton Mifflin Co., 1970.

Hogue, Charles L. (1992). Insects of the Los Angeles Basin (2nd ed.). Los Angeles: Natural History Museum of Los Angeles County.

McGavin, George C. (2000). Insects Spiders and Other Terrestrial Arthropods. London: Dorling Kindersley.

Milne, Lorus & Milne, Margery. National Audubon Society: Field Guide to North American Insects & Spiders. New York: Chanticleer Press, Inc., 1980.

© Peter J. Bryant. Text © Britton Jacob-Schram.
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