Killer hornets are being blamed for killing more than 40 people in central China, painful deaths that are forcing authorities to set up special medical units and warn rural residents to stay out of the woods. But what’s going on here? Are the hornets being upset by loggers, climate change, chemical sensitivity or is it just the victims’ bad luck to run into their nests?

Scientists who study insects say that Vespa mandarinia, or the Asian giant hornet, is not on the warpath, but it’s likely been disturbed by a spate of warmer weather as well as human disturbance of their habitat.

James H. Carpenter, curator of hymenoptera at the American Museum of Natural History in New York, has collected the giant hornets from the tropical forests of Vietnam.

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“You see them flying around and you think they are hummingbirds,” Carpenter said. “When they sting, they can draw blood. They are pretty nasty.”

Reports from various news agencies have quoted local authorities in China as stating that more than 1,600 people have been injured and 41 dead since July. The authorities say the hornets’ migratory pattern has been disturbed by unusually warm weather. There are also reports than some victims were stung more than 200 times.

Some news reports are also trying to tie the hornet attacks to climate change. Carpenter, one of the world’s leading experts on hornets, is skeptical. First off, hornets don’t migrate. He also says that their range has not been expanding and that they currently exist in both temperate and tropical regions of Asia in a wide swath from India to Korea and Japan, south to the Malaysian Peninsula and north to the Russian province of Ussuriland.

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Carpenter also noted that these hornets would run out of venom before stinging 200 times. Several victims have reportedly died of kidney failure.

One explanation could be that rural residents of Shaanxi Province, where the attacks are reported, are slowly moving into places where these hornets remained undisturbed for generations.

“My impression is the attacks are occurring in the forested areas,” said James Whitfield, an entomologist at the University of Illinois. “People are starting to go into these areas and are becoming exposed to the nests. It’s not like (the hornets) have become different than before. But the number of times they interact with people has gone up.”

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Could they reach the shores of the United States like so many other non-native insects?

Carpenter doubts it because the giant hornets’ behavior is to attack and destroy the colonies of other social insects, like honeybees. They then use the bees brood as food for their own young. That behavior would make it difficult to expand to a completely new continent. The smaller and less ferocious European hornet, which arrived in the U.S. in the 19th century, has since spread throughout the South and Midwest.

Still, cargo inspections for insects and other invasive pests are declining and probably will get worse, according to Lynn Kimsey, professor of entomology at the University of California, Davis. She noted that responsibility for these border checks has shifted from the U.S. Department of Agriculture to the Department of Homeland Security.

“All kinds of stuff is coming through and they aren’t really paying attention,” Kimsey said. “If it doesn’t explode, shoot or have a beard, they don’t pay attention. We are seeing a lot of pests coming through that aren’t being intercepted. Now with the (federal) shutdown, nobody is inspecting.”