Scientists are confronting an unsettling phenomenon at a monarch sanctuary along the Central Coast.
The Monarch Grove Sanctuary in Pacific Grove has discovered some of the butterflies still flying around – without abdomens, according to the Santa Cruz Sentinel.
“We find monarch butterflies that are missing abdomens early in the morning. Seemingly something’s eating them just before sunrise,” Nick Stong, education manager of Pacific Grove Museum of Natural History, told KSBW. “... They still have their brains and legs and everything so they can still move around a little bit.”
This had led to these monarchs being called “zombie butterflies.” The butterflies die, sometimes after a few hours, according to SFGate.
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“Their abdomen is just severed clean off, like you took it off with a scalpel,” Stong told the Sentinel.
The phenomenon is apparently being witnessed in Santa Cruz, up the coast, as well, the Sentinel reports.
Last year, scientists and volunteers discovered 200 affected monarchs in the Pacific Grove area, out of about 17,000, while they’ve found 77 thus far this year, according to Stong.
Predators enjoy the abdomen of monarchs because it has a higher fat content, according to Emma Pelton, a conservation biologist at the Xerces Society for Invertebrate Conservation.
Scientists have been stumped about which predator is attacking the butterflies.
There’s a long list of possibilities: an array of birds including Steller’s jays, crows and chickadees, along with rodents including voles, mice, squirrels and rats. Then there are wasps that attack in this manner, but only during the day, Art Shapiro, a UC Davis professor of biology and ecology, told the Sentinel.
Monarch numbers have dwindled since the 1980s.
“It’s gone down from 10 million (during the 1980s) to 300,000,” Cheryl Schultz, an associate professor of biological sciences at Washington State University, told SFGate. “That’s why we were so shocked. We did not expect it to be that sharp of a decline.”
The U.S. Fish and Wildlife Service was stunned by the estimated 75 percent decrease in the western monarch butterflies’ population since the early 2000s.
Top factors behind the butterflies’ decline include climate changes affecting food sources and habitat loss.