Icehouse Canyon, Mount Baldy, Los Angeles County, CA. © Peter J. Bryant.

Golden Hairstreak
(Boisduval's Hairstreak)

Habrodais grunus

Lepidoptera: Lycaenidae

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Cuyamaca Rancho State Park, San Diego County, CA. 7/9/11. © Diane Brodeur.

Cuyamaca Rancho State Park, San Diego County, CA. 7/9/11. © Diane Brodeur.

Characteristics: Ventral wing golden-brown, with very faint markings. Dorsal forewing golden-tan with brown suffused margins. Forewing length: 15-17 mm.

Habitats, Behavior: Boisduval's Hairstreak almost always occurs on its larval foodplant. Like many lycaenids, this species perches (particularly the male). The perching male investigates passing butterflies, even when the passer-by represents another species. Usually perching on high, protruding branches, the butterfly is hard to reach as well as inconspicuous to the collector. Adults fly most actively in the early morning or late afternoon, and only then have I observed them away from their oak haunts, nectaring at the blossoms of Wild Buckwheat (Eriogonum fasciculatum) or "puddling" at damp streamside sand or mud.

Distribution: I found grunus to be relatively common in the Santa Ana Mountains on Nat. For. Rd. 3S04 just east of Trabuco Peak. Canyon Oak, the foodplant, is common here. Lawrance Kerr (1918) also lists grunus as occurring in Irvine Park, an unusually low elevation record. Jack Levy found grunus common in July 1976, along Nat. For. Rd. 5S16 up to Santiago Peak. Boisduval's Hairstreak often flies with the California Sister (Adelpha bredowii californica) as both utilize the same foodplant.

Flight Period: Single brooded. The flight period extends from June to August.

Larval Foodplant: The sole foodplant is Canyon Oak (Quercus chrysolepis) which grows throughout higher elevations of the Santa Ana Mountains. This oak species can be distinguished from other native oaks by examining the young leaves, which are stiff, bluish-green above and covered with a yellow powdery material below. Young acorns are usually covered with a yellow powdery fuzz (Peterson, 1966). The large thick-walled acorn cups are also covered with a golden-yellow felty material, hence the species is also referred to as Goldencup Oak.

Other Remarks: The butterfly can be located by tapping branches of the Canyon Oak. If grunus is present, it will immediately flutter around, usually alighting on a nearby branch (hopefully a low branch). Boisduval's Hairstreak is no doubt much more common in the Santa Ana Mountains than seems evident from the sparse records. It is often overlooked on account of its strange habits. A local lepidopterist might try to clarify the distribution of grunus in Orange County, paying particular regard to the lowest elevations that it inhabits.

From Orsak, L. J. (1977). The Butterflies of Orange County, California. Center for Pathobiology Miscellaneous Publication #3. University of California Press, New York. 349pp.

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