California Tortoiseshell
Nymphalis californica
Description 1 7/8-2 3/8" (48-60 mm). Wing margins ragged. Above, rich russet with black blotches on FW, small
white spots on FW costa, black and white pair of spots on HW costa, margin dark often with hint of blue. Below, dull barklike brown, lighter outwardly, contrasting with darker base; margin lined with deep blue marks. FW tailing edge straight.
Similar Species Compton Tortoiseshell larger, has silver "V" on HW beneath, and heavier black spotting above. Anglewings have narrower, more ragged wings and concave trailing FW edge.
Life Cycle Caterpillar velvety black with yellow and blue-black spines and white specks. Chrysalis gray and tan, may have blue cast; horned head. Various buckthorns (Ceanothus) are host plants; probably also other plants.
Flight 1 brood in North, 2 or 3 farther south; adults may be encountered year-round.
Habitat Mountainous terrain below subalpine zone, especially canyons; also lowland forest edges, glades, and parklands.
Range British Columbia south to S. California, and east in mountains to Saskatchewan, Nebraska, and New Mexico; very rarely wandering or introduced into Midwest and Northeast.
Discussion Some biologists consider this the same species as the European Large Tortoiseshell (N. polychloros), which feeds on elms (Ulmus). Both appear irregularly. Although much more common on the whole than the Compton, the California Tortoiseshell may be rare or absent from large parts of its range for several years. These dearths are followed by periods of enormous abundance, involving emigrations over immense areas, which seem to be related to population pressures, host plant availability, and climate conditions.
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