The California Tortoiseshell is a bright orange-and-black butterfly of western mountains that periodically irrupts in enormous numbers — millions of individuals migrating through mountain passes together. Adults overwinter and emerge early in spring, feeding on tree sap and early flowers. Caterpillars feed gregariously on California lilac in dense colonies.
Best time to see a California Tortoiseshell
The best time to see a California Tortoiseshell is March–July, when about 67% of U.S. sightings happen, based on 20,420 research-grade iNaturalist observations.
Not certain it is a California Tortoiseshell? What bug is this? walks through what to check first and the lookalikes that catch people out.
Recent California Tortoiseshell sightings near you
Live, research-grade observations from iNaturalist. Allow location to center the map on you.
Spotted a California Tortoiseshell?
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