Mass-migrant
Guides
Nymphalis californica
California Tortoiseshell, Cal Tortie
The California Tortoiseshell is a medium-sized brushfoot butterfly known for its mass migration events that can occur at irregular intervals. Adults overwinter and may be seen sunning on mild winter days. The species is notable for its seasonal altitudinal migration pattern and its ability to defoliate stands of Ceanothus host plants during population outbreaks.