CREATURE FEATURE : Fall of the Monarchy

Are we down to the last butterfly? In the past few years, the number of Western monarch butterflies coming to California has dwindled alarmingly. In previous winters, more than a million migrated from other Western states; this year, scientists say, the count was down by 95%.

“About 15,000 monarchs usually show up at Camp Pendleton,” says David Marriott, founder of the Encinitas-based Monarch Program, which studies the insect’s migration. “This past winter, there were about 1,000. I was shocked; the drop was so drastic.”

Scientists have no solid explanations, but Marriott is looking at the role of a protozoan spore that has infected up to 60% of monarchs at several of the state’s 250 wintering sites. The spore lives on milkweed, a favorite food of monarchs. Once ingested, it attacks the butterfly’s wings and exoskeleton and can turn a chrysalis, which in a healthy monarch resembles a gold-speckled green bullet, into a pallid lump. Marriott is testing the effectiveness of spraying tetracycline on the milkweed, hoping that monarchs that munch on the antibiotic-laced plant will be able to resist the spore.

But Marriott is hoping that the decline is merely cyclical. “I would think monarchs have pretty much bottomed out,” he says. “I think they’ll start rising again.”