Butterfly deaths are just nature being nature

Every year, 25,000 monarch butterflies migrate to Pacific Grove on the Monterey Peninsula. This year, something is killing off hundreds of them.

Alarmed visitors to the Pacific Grove Museum of Natural History are reporting butterfly carcasses on the ground, all missing their abdomens. Enough hay was raised to prompt the Museum and the City of Pacific Grove to issue a joint statement about the butterfly deaths.

The word? Just nature at work. Consider: Butterflies can’t fly unless the air temperature is at least 55˚ F. Cooler nights and mornings recently have grounded the Monarchs longer each day, leaving them susceptible to predators like rodents, birds, and the number one suspect: wasps.

The missing abdomens are a signature of wasp attacks, say biologists, who add it’s difficult to tell if the wasps acted alone or had help. Either way, they say it’s not unusual.

300 dead monarchs have been observed, though the numbers in the overall grove are still healthy, with more than 8,800 monarchs still hanging at the sanctuary.

The Museum advises visitors to plan seeing the grove between 12 and 3 on “warmer” days when the butterflies are active. Temperatures are expected to be on the cool side this week in Monterey.

Jesse Garnier

Jesse Garnier is the editor and founder of SFBay. A Mission District native, he also teaches journalism as associate professor at San Francisco State University.