The race is on to keep Asian giant hornets from spreading in the Pacific Northwest.
Since 2019, 12 of the hornets — five trapped and dead, the rest photographed but escaped — have turned up in Washington state. That includes three recently reported in Whatcom County, Wash. Others have been found in British Columbia, Canada.
“We’re pretty sure there’s at least one nest” somewhere near Birch Bay along the Washington coast, says Karla Salp, a spokesperson for the Washington State Department of Agriculture in Olympia.
Efforts are under way to catch a live hornet, attach a radio tag and track it back to a nest, Salp says. The plan is to destroy the nest, hopefully before hornets that can start nests of their own hatch. That usually happens in mid to late October, she says.
That eradication effort was already urgent thanks to the insects’ reputation: The world’s largest hornets (Vespa mandarinia) have been dubbed “murder hornets” in part for their deadly assaults on honeybees (SN: 5/29/20). Now a new study maps where the giant hornets could spread if left unchecked.
Asian giant hornets thrive where it’s mild and rainy — and that makes large swaths of the Pacific Northwest prime real estate for them. Farther afield regions of the United States — including along the East Coast — could potentially support the hornets, but it’s unlikely the insects could fly that far on their own, researchers report online September 22 in the Proceedings of the National Academy of Sciences.
The mapping efforts are important because “we really don’t know anything about how this species spreads,” says Chris Looney, an entomologist with Washington’s agriculture department. Details like how fast the hornets can fly and how their preference for underground nests affects their potential to spread are unknown, he explains. “That’s the kind of maddening lack of information that makes responding to this species so challenging.”
But by looking at what sorts of habitat conditions — including rainfall and temperature — the hornets prefer in their native range in Japan, South Korea, China and several other East Asian countries, Looney and colleagues mapped regions of the United States where the hornets might be able to survive. Then, the researchers simulated the insects’ spread using information on how the Asian giant hornet’s smaller relative, V. velutina, has invaded Europe. That hornet spread at an average rate of about 100 kilometers per year.
“There is a considerable amount of suitable habitat along the West Coast and our dispersal simulations of how quickly the invasion might spread were surprising to us,” says David Crowder, an entomologist at Washington State University in Pullman.
Simulations of a worst-case scenario showed that about half of both Washington and Oregon offer suitable habitat. The hornets could reach Oregon on their own in 10 years. In 20 years, the hornets could reach eastern Washington and farther into British Columbia. Parts of Northern California and northern Idaho are at risk, too. And while much of the eastern United States has suitable habitat, “it is highly unlikely, if not impossible, that the hornet could traverse the continent on its own, given the lack of suitable habitat in much of the central U.S.,” Crowder says.
Still, this research is “telling a more positive story than it’s being made out to be,” says entomologist Douglas Yanega from the University of California, Riverside. “They’re talking about two decades before [the hornet] will reach the limits of its distribution. That’s a very long time.”
And, he notes, there’s still time to stop the insects in the United States. “The actual number of colonies out there is so small that if we can find a few of those colonies, we might be able to completely eradicate them,” Yanega says. “It doesn’t look like the kind of situation that’s capable of exploding on us, and it certainly hasn’t so far.”