Science / Medicine : Butterfly Population Soars

We can thank the early winter rains and the following drought months for the millions of butterflies fluttering around California, according to UC Davis zoology professor Arthur M. Shapiro.

“This is a tremendous year for butterflies,” he said. “I’ve been keeping butterfly records for Northern California for 17 years, and this is the earliest spring in those years for most butterfly species, and their populations are extraordinarily large.”

Shapiro said species appearing in large numbers include the California tortoise shell silvery blue, the California sister, the common white cabbage, the anise swallowtail and the painted lady.

The butterflies benefited from December-January rains that brought out fodder that the insects nibble on. The warm, dry weather that followed did not allow for the growth of bacteria that usually thin the butterfly population.

Shapiro said that a similar butterfly explosion occurred in the first year of the 1976-77 drought. However, the butterfly population dwindled in the drought’s second year because of unfavorable food conditions.

Shapiro said the front of this year’s painted lady migration hit the Sacramento-Davis area in mid-March, with an estimated 9.5 million of them crossing the area between Sacramento and Fairfield since then.

He noted that the current migrants are laying eggs as they fly north. He said a new brood could be hatched and flying by next month, and a third generation could arrive before the painted lady migration ends in the Northwest in the summer.