Where have all the butterflies gone?

Cold, wet conditions early in the year have caused the summer of 2006 to be the worst season for California's butterflies in almost four decades, reports Art Shapiro, professor of evolution and ecology at the University of California, Davis.

"It [was] the worst spring for butterflies of my 35 in California," Shapiro affirms. "There will probably be long-term repercussions, especially for species already in serious decline."

Shapiro says that, at most of his study sites, he has seen half or less than half the number of species present at this time in an average year, and far fewer individual butterflies than usual.

Last winter's weather conditions may have a lot to do with the drop in numbers. The early winter was mild, with not enough cold to end the winter dormancy or "diapause" of most butterflies, so they did not emerge to take advantage of the early warm weather in February. Then March turned cold and wet, wiping out the breeding of species that had emerged. While Northern California was soaked, the southwest desert had a very dry "La Nina" winter, leaving little food for the caterpillars of the painted lady. As in previous dry winters, the painted lady butterflies had given up on trying to breed in the desert and headed north.

Apart from this year's weather, several species of butterflies, including the large marble, sooty wing, Lorquin's admiral, and the mourning cloak suffered major declines in 1999 and have not yet recovered. Shapiro compares the setbacks of butterflies to similar drops in populations of frogs and other amphibians. He is working to test various ideas about why these butterflies are in danger, including combinations of changing climate and altered land use.

In the short term, butterfly species that breed several times a year may rebound quickly to take advantage of improving conditions. For species with only one brood per year, however, a catastrophic season will have repercussions for up to a decade.

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