Monday, March 19, 2007

California Tortoiseshells


A flurry of butterflies unexpectly appeared at the UC Botanical Garden on March 12. I counted ten, but I am sure there were more. They particularly liked the shady area on the side of a building. I observed one with its proboscis out, probing the painted surface. What was it doing? The butterflies turned out to be California Tortoiseshells, which overwinter as adults
in lowland California. The one to the left is clearly tattered, as if it is at least several months old. They become active and lay eggs on Ceanothus when the weather warms. I haven't been able to detemine whether we can expect eggs and caterpillars in the Garden. Some authorities say that they go through one generation in lower elevations before they migrate to the Sierra, others say they migrate without laying eggs. I may be seeing the caterpillars eating and growing the the California section of the Garden where the ceanothus grows. I will certainly be looking for them. . At any rate, after one or two generations in the mountains, they migrate back to
the coast to spend the winter. The California Tortoiseshell, native to many states in the western United States, is a beautiful orange butterfly with dark borders and black spots. They have now abandoned the building, as far as I can tell.
The population of this butterfly sometimes explodes. When I was driving through Yosemite in the early 1970s, I killed dozens on the windshield without meaning too. Sometimes there are so many that cars skid on the slimy dead bodies on the road and drivers have to stop to clean their windshields. I saw so many in the UC Botanical Garden, I think this could be a big year.