3/4-1 1/4" (19-32 mm). Spring brood deep silvery violet-blue above, female has coal-black FW border; below, slate-gray, black checkered border, and variable black HW interior spotting with marginal spotting small and fading toward FW. Summer brood blanched violet-blue above, with pale white basal half to FW and most of HW; female black bordered and much whiter; below, washed out pale white with faint markings.
Sooty Azure similar below but blackish above with little blue. Arrowhead Blue has white arrowhead in HW cell below.
Egg pea-green; laid in flowers and buds. Caterpillar highly variable; usually cream-colored, daubed rosy, checkered on dusky back and green side slashes. Many flowers are host plants
, especially dogwoods (Cornus), viburnum (Viburnum), ceanothus (Ceanothus), blueberries (Vaccinium), black snakeroot (Cimicifuga racemosa), and meadowsweets (Spiraea). Plump, golden-brown chrysalis overwinters.
Multiple broods on East Coast; March to mid-April, May-June, mid-July to August. Fewer northward, perhaps more to South; 1-2 broods in West.
Open deciduous woods, roadsides, and brushy areas from sea level through mountains; clearings, glades, and many other places in and near woodlands.
Alaska east across Canada, and south through entire U.S. to Mexico and Panama in mountains.
Widespread and common in early spring, Spring Azures signal the return of warm weather. This species presents a complex set of identities to entomologists; only recently was the Sooty Azure recognized as a separate species. Genetic and biological evidence suggests several distinct butterflies still remain within the broad definition of the Spring Azure. A darker, bluer, highly polymorphic first brood produces chrysalises which may overwinter or emerge the same year. Chrysalises from the first of the paler, single form, late spring and summer broods will hatch several weeks later, with the last ones of later summer overwintering. The caterpillars of different broods feed on different plants depending upon what is flowering at the time. For many years the Spring Azure was known by the scientific name C. argiolus, which is now considered a related Old World species. Current nomenclature reestablished the 18th-century name.