California Tortoiseshell (Mt. Diablo Butterflies)

California Tortoiseshell

Nymphalis californica

General description ⁶

Most similar to the Compton Tortoiseshell (Roddia l-album = N. vaualbum), but californica has a black dorsal hindwing margin, not heavily marked with orange-brown as in l-album. There are no described subspecies; the name herri mentioned by Bird et al. is a cool-weather induced phenotype according to Guppy & Shepard (2001). There appears to be little geographic variation in this species, possibly due to the fact that it is able to migrate long distances, resulting in mixing of populations.

Life cycle ⁷

The cylindrical, yellow-green eggs have vertical ridges. The mature larva is velvety black with two diffuse, yellow dorsal lines and orange-brown, branched spines (Guppy & Shepard 2001). Like the Compton Tortoiseshell, this species is very rare or absent in some years; it is unclear if all Aberta records represent migrants (spring) or offspring of migrants (fall). It is possible that californica is able to overwinter in the greater Waterton area wher the larval food plant occurs, although Guppy & Shepard (2001) suggest southern interior BC populations must be maintained over the long term by migrants from the south. Alberta records outside of the Waterton region certainly represent migrants, since the larval food plant does not occur elsewhere in the province.