In Washington State we have ten species of butterflies which are loosely grouped as “checkerspots” owing to the cancellate or squarish patterning of intersecting lines on the wings. Our checkerspots are scientifically grouped into three separate genera, Euphydryas, the “true checkerspots” to many lepidopterists, Phyciodes, also known as the “crescents” and including this species, and Chlosyne, the remaining checkerspots. The genus Euphydryas can be distinguished by the very straight leading edge of its forewings, and Phyciodes can be distinguished by the presence of a distinct light-colored crescent-shaped mark near the outer margin of the ventral hindwing. Chlosyne lacks the crescent-shaped mark.

Phyciodes pallidus is found only in western North America, from SE British Columbia through the interior to northern Arizona, west to Nevada and east to eastern Wyoming. This is a relatively rare species in Washington, occurring only east of the Cascades in shrub-steppe habitat. Occurrences are in small isolated colonies primarily in northern Okanogan County, also along the Columbia River just south of the Okanogan. There are also colonies along the Snake River north and east of the Blue Mountains and in a few spots along the Columbia River in Klickitat County.

The Pale Crescent has a short flight period in Washington, found on the wing from early May to early July, and is single-brooded throughout its range. After mating the female lays large masses of eggs in late May on its native thistle host plant, typically Cirsium undulatum, Wavy-leafed Thistle. Eggs are laid on the underside of the thistle leaf, apparently always on younger (but not necessarily small) plants which do not yet have flower stalks. The eggs hatch ‘en masse’ and the young larvae live communally in very loosely- woven silk nests usually in a fold of the thistle leaf. First and second instars bore completely into the thistle leaves where they remain out of sight while feeding on the internal layers, but later instars are too large to remain inside the leaves and stay on the surface. Each larva is tethered with a single strand of silk, an- choring it to the communal nest or adjacent thistle leaf. The larvae are supposed to diapause from late summer through the winter in the 2nd or 3rd instar, however when reared in captivity up to a third of the larvae may develop through to the pupal stage and eclose to 2^nd brood adults while the remainder diapause as predicted. When the thistle host plants develop fresh growth in the spring the surviving larvae disperse to feed. If disturbed the larvae coil into a ball and tumble to the ground as a predator-escape response.

Phyciodes pallidus adults are often confused with the very common Mylitta Crescent. Mylitta can usually be differentiated by size, being much smaller than P. pallidus, however one some-

times encounters very large female Mylittas so this character alone is unreliable. Dorsally, females of the two species are almost inseparable, but males of P. pallidus are characterized by fewer lines and markings, the dorsal hindwing in particular being less heavily marked, often with a large clear patch. Ventrally the two species are more easily separated, P. pallidus being much lighter in color than P. mylitta. In P. mylitta the VHW is boldly marked with contrasting dark and light bands, and the “crescent” along the border is surrounded by dark coloration causing it to stand out strongly. In P. pallidus the VHW is much lighter with only subtle banding and the crescent is only mildly accented by slightly darker surrounding scales.

Pale Crescents are found only in dry shrub-steppe habitats where native thistles grow. Males eclose and fly before females, and adults of both sexes can be found nectaring on flowers. Adults seeking nectar may wander a short distance from their larval host plants but are more easily found in close proximity to their native thistles. Males perch conspicuously, challenging all fliers-by searching for mates, but the females are much less conspicuous, usually remaining low in the vegetation.

(All photos this page by David Nunnallee.)

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