What Are Murder Hornets?
Many of the most dangerous and destructive pests in the United States are foreign insects unwittingly introduced to North America. Murder hornets, also known as Asian giant hornets, have joined this list of exotic insect threats. Stopping this invasive pest is vital for North America's ecosystems and economy. By staying informed and learning why murder hornets are so dangerous, you can do your part to help control these pests in the U.S.
What are murder hornets and what do they look like?
Known by the scientific name Vespa mandarinia, murder hornets are the world's largest hornet species. One of only 23 true hornet species — none of which are native to North America — they're the only giant hornet species in the world. Murder hornets are native to East Asia, where they're well established in Korea, Japan and other areas. They go by many common names including Japanese hornet, yak-killer hornet and giant sparrow bee.
Typical murder hornets measure 1.5 to 2 inches long, but queens can grow even larger. Their open wings span 3 inches or more. These distinctive hornets have broad, orange-yellow heads with large mandibles and dark, prominent eyes. Murder hornet bodies have a black thorax and a pinched, wasp-like waist. Black and orange-yellow stripes encircle the abdomen. The stinger, found only on females, is about 1/4 inch long.1,2
A murder hornet's size and distinctive markings simplify identification.
Photo credit: Apsdake, CC BY-SA 3.0
How do murder hornets spread?
No one knows how murder hornets got to North America. Scientists suspect a few of these ground-nesting insects arrived hidden in international cargo. The first North American sightings were in British Columbia in August 2019. Four months later, Washington state confirmed two Asian giant hornet reports. Studies indicate the Canadian and U.S. hornets represent separate, unrelated introductions.1
In May 2020, murder hornets were again confirmed in British Columbia and Washington state, suggesting these pests can survive North American winters. Though earlier Washington sightings involved nonreproductive worker hornets, the May 2020 specimen was an Asian giant hornet queen. This suggests a reproductive hive existed the previous year.1
Like yellow jacket wasps, murder hornets establish new nests annually. A single reproductive hive produces 200 to 300 new queens each year. Queen hornets overwinter in soil or sheltered hollows, then disperse in spring to start their own subterranean colonies. Scientists aren't sure how far murder hornet queens disperse, but related species travel up to 20 miles.2
Asian giants hornets may feed on fruit early in the year.
Why are murder hornets considered harmful?
If murder hornets establish in North America, their presence threatens the environment, native ecosystems, agricultural economies and public health. In early summer, new worker murder hornets start foraging to feed their colonies. All large insects are potential targets, from beetles to caterpillars, but honeybees suffer the worst fate.
At first, worker murder hornets attack honeybees sporadically, killing a few adult bees for food. But in late summer, murder hornet behavior changes. The workers attack and slaughter entire honeybee hives in just a few hours. Bees are lured from the hive and decapitated, their bodies left piled on the ground. Then the hornets move in and plunder honeybee eggs, larvae and pupae to feed their growing hornet colonies.1,2
Native Asian honeybees have natural defenses against Asian giant hornets. But the honeybee species responsible for pollinating U.S. agricultural crops is a European native. Roughly the size of a murder hornet's thorax, a European honeybee is defenseless against these predators. With U.S. honeybee populations already struggling, giant hornet attacks could be devastating. Scientists believe native insects are also at risk.2
Murder hornet stings add another danger. When threatened, murder hornets sting to defend their nests and hijacked honeybee hives. Murder hornet venom is comparable to common bees and wasps, but their stingers don't detach. These giant pests can sting repeatedly, delivering large quantities of toxic venom and extremely painful stings.
If you're stung by an Asian giant hornet, chill the site with ice to slow the venom's spread, then get to a hospital. In Japan, 30 to 50 people die from Asian giant hornets each year.2
Murder hornets grow up to 2 inches (5 centimeters) long.
Photo credit: Yasunori Koide, CC BY 4.0
How can I protect my family against murder hornets?
One of the best defenses against murder hornets is staying informed about this pest's status in the United States. If you suspect a murder hornet nest, stay at least 10 feet away. Don't approach it or attempt to remove it. Instead, contact your state department of agriculture or state apiarist immediately. If you find a dead murder hornet, contact authorities and collect the specimen so they can study it further.1
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1. Washington State Department of Agriculture, "New Asian Giant Hornet Sighting in Washington State - WSDA Virtual Press Conference," May 29, 2020.
2. Washington State Department of Agriculture, "Asian Giant Hornet in the Pacific Northwest - Feb 2020," March 4, 2020.