How 'murder hornets' came to the U.S.

The Asian giant hornet, an invasive species recently dubbed the "murder hornet" in the U.S. that's known for beheading and slaughtering honey bees, has arrived in Washington state. But it's still unknown how many hornets there are (sightings are few), or how they traveled into the country.

"We don’t know exactly how it arrived here," said Timothy Lawrence, an associate professor in the Department of Entomology at Washington State University.

But insect experts have a pretty good idea — though definitively proving it might be impossible. Though there are a number of potential explanations, a queen hornet may have hitched a ride on a container ship traveling across the Pacific Ocean, suggested Lawrence.

This is almost certainly what happened, said Tim Kring, the head of the Virginia Tech Department of Entomology. "How many ships land on the West Coast every day?" Kring asked, rhetorically.

Three of the five busiest ports in the U.S. lie on the West Coast, including Washington's Northwest Seaport Alliance. The container ships that pull into these ports can teem with insects, noted Kring. Sometimes ships in the U.S. must even be fumigated due to infestations. Most invasive insects that entomologists track come from human trade, noted Kring. We give the bugs the ability to go places they can't fly or hop on their own, thousands of miles across the ocean.

Washington ecologists, however, weren't really on the lookout for the Asian giant hornets, an insect that grows some two inches long and wields venom more toxic than a bees'.

"No one really saw this one coming," said Lawrence.

They were more focused on monitoring Asian honey bees. They carry a mite that's proven deadly to Western honey bees (aka European honey bees), whose populations are already dropping due to parasites and pesticides. Now, there's the potential of a problematic infestation of Asian giant hornets in the northwest corner of Washington (home to honey bees), and potentially beyond. Besides producing honey, honey bees pollinate over 100 crops in the U.S.

"The honey bee is already facing a lot of threats and we clearly didn't need another one," said Lawrence.

The potential impact of these bee-killers on the U.S. honey bee industry is still unknown. But in some places it could be a devastating punch to an already struggling industry.

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To colonize the U.S., just a single queen Asian giant hornet, already inseminated, would have needed to find a little cubby to hide in on a ship, explained Virginia Tech's Kring. After mating in the fall, queens store sperm and can then start a colony that spring.

It is possible, however, people brought Asian giant hornets to the U.S. intentionally, said Lawrence, perhaps even to spice up cocktails.

In an email, a public affairs representative for the Washington State Department of Agriculture said the agency can't explain definitively how the hornets arrived. "We really don’t know," the agency said. "Invasive species are introduced in many ways. Certainly through the ports/waterways is one option, but we couldn’t say."

Yet a hornet hitching a ride on a container ship is most plausible, emphasized Kring. In fact, the hornets may have previously traveled to the U.S., but just didn't successfully establish a colony — so we didn't know they'd made it. "I would bet there's been introductions other times," said Kring.

It wouldn't be hard to hide on a giant ship, loaded with crates.

"My hypothesis would be that a mated queen happened to be present in the packaging of some trade product, which is thought to be how most of the recent invasive insect species from Asia arrived," said Theodore Burk, an entomologist at Creighton University. A queen is "likely to seek shelter in any promising cavity, and a shipping crate or something similar would work just fine," Burk added.

Yet, no matter how the invasive wasps arrived in the U.S., insect experts say they should be eradicated. "If we can find the nest and destroy them, that would be ideal," said Washington State's Lawrence. "If it gets established, it will be extremely difficult to eradicate."

Invasive insects are frequently trouble. They can kill native trees by the millions (like the emerald ash borer beetle), threaten agriculture and damage plants (spotted lanternfly), and spread disease (Asian longhorned ticks).

"All of them are a problem," said Kring. "[Asian giant hornets] just hit the public eye."