Attack of the Giant Hornets

Nobody knows how Asian giant hornets reached North America. They might have nested in packing material used to ship international cargo, says Todd Murray, an entomologist at Washington State University. Some people eat the wasps’ larvae, or immature young, as a delicacy. So the bugs also could have been smuggled over intentionally, adds Murray.

Asian giant hornets can grow up to 5 centimeters (2 inches) long—four times larger than a yellow-jacket (see Humongous Hornets). When attacked, a giant hornet uses its extra-long stinger to inject toxic venom into its foe. “Because they’re so large, they can inject a large volume of venom,” says Murray. People have compared the pain of a giant hornet sting to having hot nails driven into their skin. Repeated stings have occasionally caused fatal allergic reactions in people, earning the insects the nickname “murder hornets.” But human deaths from the bugs are extremely rare. The real threat isn’t to people—it’s to honeybees.

How did Asian giant hornets reach North America? Nobody knows. They might have nested in packing material used to ship international cargo, says Todd Murray. He’s an entomologist at Washington State University. Some people eat the wasps’ larvae, or immature young. They’re considered a fancy food. So people could also have smuggled the bugs over on purpose, adds Murray.

Asian giant hornets can grow up to 5 centimeters (2 inches) long. That’s four times larger than a yellow jacket (see Humongous Hornets). A giant hornet uses its extra-long stinger when attacked. It injects toxic venom into its enemy. “Because they’re so large, they can inject a large volume of venom,” says Murray. People say a giant hornet sting feels like having hot nails driven into their skin. At times, repeated stings have caused fatal allergic reactions in people. That’s why the insects are nicknamed “murder hornets.” But human deaths from the bugs are very rare. The real threat isn’t to people. It’s to honeybees.

In the fall, Asian giant hornet workers seek out beehives. They kill a few bees, chewing their bodies into “meatballs” that they carry back to the nest to feed their young. Then the hornets might swarm the hive and kill every bee inside. About 20 hornets can slaughter tens of thousands of bees in a matter of hours, says Murray.

That’s a huge problem because honeybees are important pollinators. The bees carry pollen between plants as they feed, allowing the plants to reproduce. Approximately one-third of the food Americans eat comes from plants pollinated by honeybees. Food production could suffer if the Asian giant hornet becomes an invasive species—a non-native organism that spreads uncontrollably (see Other Invasive Species).

In the fall, Asian giant hornet workers look for beehives. They kill a few bees and chew their bodies into “meatballs.” They carry these back to the nest to feed their young. Then the hornets might swarm the hive and kill every bee inside. About 20 hornets can quickly destroy tens of thousands of bees, says Murray.

That’s a huge problem because honeybees are important pollinators. The bees carry pollen between plants as they feed. This allows the plants to reproduce. About one-third of Americans’ food comes from plants that honeybees pollinate. Food production could suffer if the Asian giant hornet becomes an invasive species. That’s a non-native organism that spreads out of control (see Other Invasive Species).

To prevent a giant hornet invasion, WSDA scientists asked the public to report sightings of the bugs. With help from local beekeepers, they set more than 2,500 traps to catch the wasps. 

In September, WSDA entomologist Chris Looney visited a homeowner near Blaine who had found multiple dead hornets in his traps. Just as Looney was about to leave, a live hornet flew by. He caught it with a net. “I called everybody and said, ‘We found one! Let’s try to track it,’” he recalls.

WSDA scientists needed to stop a giant hornet takeover. So they asked the public to report sightings of the bugs. They set more than 2,500 traps for the wasps. Local beekeepers helped.

A homeowner near Blaine found multiple dead hornets in his traps. So WSDA entomologist Chris Looney went there in September. As Looney was leaving, a live hornet flew by. He caught it with a net. “I called everybody and said, ‘We found one! Let’s try to track it,’” he remembers.

If scientists could follow the hornet, it would lead them right to its nest. The next morning, they tried gluing a wireless tracking tag to the hornet’s body. Unfortunately, that prevented it from flying. The next week, they tried again with another captured hornet. This time they tied the tag on with dental floss and fed the hornet berry jam for energy. It took off, and the scientists followed it for about 300 meters (1,000 feet). But the hornet flew so fast that it quickly moved beyond range of the device used to communicate with the tag, and the scientists lost the signal.

In October, the team caught more live hornets and tried longer-range tracking tags. One hornet chewed through the dental floss right after the scientists tied it on. Another nearly outflew them again. But as the scientists wandered the forested area where the insect had disappeared, their device picked up a faint signal from a tag. They followed the signal to a large tree. There, they heard a hornet buzz overhead and watched it fly into a crevice in the tree trunk. They’d found the nest! “We were pumped,” says Looney.

Scientists hoped to follow the hornet. It could lead them right to its nest. The next morning, they glued a wireless tracking tag to the hornet’s body. But that stopped it from flying. The next week, they tried again with another captured hornet. This time they tied the tag on with dental floss. They also fed the hornet berry jam for energy. It took off, and the scientists followed it for about 300 meters (1,000 feet). They tracked it with a device that communicated with the tag. But the hornet was too fast. It quickly flew out of the device’s range. The scientists lost the signal.

In October, the team caught more live hornets. They tried longer-range tracking tags. Right away, one hornet chewed through the dental floss. Another nearly outflew them again. The scientists wandered through the forest where the bug had disappeared. Their device picked up a weak signal from a tag. They followed the signal to a large tree. There, they heard a hornet buzz overhead. It flew into a crack in the tree trunk. They’d found the nest! “We were pumped,” says Looney.

Two days later, the WSDA team returned. They arrived at the nest before dawn, when the hornets would be less active. They put on protective goggles and face shields and zipped themselves into full bodysuits made of material so thick, even giant stingers couldn’t pierce it.

After climbing 3 m (10 ft) up the tree, the scientists stuffed foam into the crevice that held the nest. Then they sealed the trunk with plastic wrap to keep the hornets from crawling out. They cut a small hole through the plastic wrap and foam, inserted a vacuum hose attached to a special collection canister, and banged on the tree to rile up the hornets. “As the wasps would come out, I would vacuum them,” says Looney.

After vacuuming for about 45 minutes, the team sealed the nest with sprayable foam and cut it out of the tree to inspect it. They determined that it had housed more than 500 Asian giant hornets, including 184 potential queens. If the scientists hadn’t found the nest before the hornets hunkered down for winter, some of those queens could have started new colonies in spring. “We caught it right in the nick of time,” says Looney.

Despite successfully eradicating this nest, the WSDA suspects there may be more out there. So, Looney and his team are staying vigilant, just in case. Luckily, no Asian giant hornets have been spotted outside of northern Washington so far. That means there’s still a chance to stop them—before they spread through the U.S. 

Two days later, the WSDA team returned. They got to the nest before dawn, when the hornets would be less active. They put on protective goggles and face shields. They also zipped themselves into full bodysuits made of thick material. Even giant stingers couldn’t pierce it.

The scientists climbed 3 m (10 ft) up the tree. They stuffed foam into the opening of the nest. Then they sealed the trunk with plastic wrap. That would keep the hornets from crawling out. They cut a small hole through the plastic wrap and foam and stuck a vacuum hose inside. It was attached to a special collection container. Next, they banged on the tree to make the hornets angry. “As the wasps would come out, I would vacuum them,” says Looney.

The team vacuumed for about 45 minutes. Then they sealed the nest with sprayable foam and cut it out of the tree. When they examined the nest, they found that it had contained more than 500 Asian giant hornets. That included 184 possible queens. The scientists were glad they’d found the nest before the hornets settled in for the winter. Otherwise, some of those queens could have started new colonies in spring. “We caught it right in the nick of time,” says Looney.

The WSDA wiped out this nest, but they suspect more may be out there. So Looney and his team are keeping watch, just in case. Luckily, no Asian giant hornets have been spotted outside northern Washington yet. That means there’s still a chance to stop them—before they spread through the U.S.