In Washington State we have ten species of butterflies which are classified as checkerspots; a common character is the cancellate or squarish pattern of intersecting lines on the ventral hindwings. Our checkerspots are placed in three separate genera, Euphydryas, Phyciodes and Chlosyne. In our area the genus Chlosyne includes three species, while Phyciodes and Euphydryas have four and three species respectively. Phyciodes spp. have a distinct light crescent mark near the outer edge of the ventral hindwing (lacking in Chlosyne), and in Euphydryas the leading edge of the forewing is straight (strongly curved near the body in Chlosyne).

The Sagebrush Checkerspot is an arid lowland species of shrub-steppe habitats, ranging from southern and eastern Canada to Montana and south to New Mexico and California. In eastern Washingon the flight period is early April to early July and is strongly keyed to the growth of the host plants. At Red Mountain in Benton County, WA, where spring typically arrives quite early, adults fly from early May to early June. However at Schnebley Coulee in Kittitas County, where spring arrives considerably later, adults fly earlier, about April 20 to May 10. Why these apparently reversed flight periods? This appears to be because different host plants are used at the two localities, the later-growing Chrysothamnus viscidiflorus (Green Rabbitbrush) at Red Mtn, but the earlier-growing Erigeron linearis (Linear-leafed Daisy) at Schnebley Coulee. The butterflies have significantly adapted their flight periods to coordinate with their host plants. While these two host plants are used by C. acastus, our other two Chlosyne species utilize different plants, mostly various tall aster species.

Chlosyne acastus flies in a single spring brood; males eclose about a week before females and are often worn by the time they mate with the fresher females. About 10 days after mating eggs are laid in large masses on the host plant, often 100- 150 eggs, on the undersides of leaves or on stems. Eggs hatch after 6 days; the young larvae feed on host leaves and are highly gregarious, using delicate communal silk nests. These nests are abandoned by L3 when the larvae revert to spines and perhaps chemicals for defense. Larvae usually overwinter as L3, however they are flexible and opportunistic and at least in captivity with prime food available some have been found to attain L5 before diapause. Post diapause (spring) larvae are solitary, often feeding diurnally and resting or sunning openly on the host plants or adjacent rocks. Adults eclose about 18 days after pupation.

In cloudy conditions or at dusk both sexes often roost in small communal groups on shrubs, especially in canyon bottoms. Males establish territories along paths or on sage slopes, challenging interlopers and pursuing females. Adults show subtle wing pattern differences from the other Chlosyne species (Hoffmann’s and Northern Checkerspots), but adult C. acastus are most reliably identified by their sexual dimorphism, males being orange and females black. Chlosyne palla (Northern Checkerspot) is the most similar, and black females occasionally occur in this species, but its range rarely overlaps with the shrub-steppe C. acastus, C. palla being a woodland-forest species.

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