• Valerie Just

Murderous Hornets

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Sound menacing? Perhaps the description conjures up thoughts of a super-villain, or an evil-doer?


Murder hornets are better known as the Asian giant hornet, and are native to east Asia and Japan. In Japan, where the insects are hunted and eaten, some 30 to 50 people die each year from their venomous and excruciating sting.


Karla Salp, a spokesperson for the Washington State Department of Agriculture, said it was unclear just how they came to the United States, but speculation is that these hornets hitchhiked a ride on a shipping container.


Two hornets were spotted in Blaine, Washington in late 2019 - one was alive and flew off, the other was dead. Since December, pest control and government agencies have received unconfirmed reports of sightings as far south as Portland, Oregon. Paul van Westendorp, an apiculturist in British Columbia, said the only actual nest of hornets found in North America was discovered on Vancouver Island and destroyed. A specimen was also found in White Rock, British Columbia, last November. Scientists suspect there are probably more of the insects than just the two spotted last year, which is why a public outreach campaign has been launched to help with eradication efforts.


"During this trapping season and with the help of public education and encouragement to report suspected sightings, we hope to have a better idea of where they are as well as to eradicate them if we can," Salp said. Scientists warn that unless the insect is eliminated in the next couple years, it could spread in North America and become permanently established.


Why the Concern?

For Beekeepers

Salp said the hornets don't usually attack people, but they are known for decimating honeybee colonies. "In general, people do not need to worry," she said. "As long as you don't step in a nest or approach a beehive they have taken over, there is a fairly low risk that you will be stung. "That being said, if you are stung, their venom is more toxic than that of local bees and wasps, and they have more of it," she added.


But while the giant hornets are typically not harmful to humans, they do pose a great danger to bee populations, which have been declining in many parts of the world. Washington State University researchers said the hornets attack the bee hives, decapitating and killing the adults and eating the larvae and pupae. The slaughter begins when a worker hornet spots a colony, marks it with a pheromone and then brings a backup crew of between two and 50 others. While a honeybee hive can have thousands of residents, hornets can wipe out the whole population in hours. During one recorded slaughter examined by researchers, each hornet killed one bee every 14 seconds, using powerful mandibles to decapitate its prey. The hornets then occupy honeybee nests for up to a week or more, feeding on the pupae and larvae.


The arrival in the United States has brought particular dread to beekeepers. They are working together to post traps to try and catch queens this spring and workers in the upcoming summer. Government biologists are trying to identify where the hornet has settled in Washington State and eradicate it before it establishes a permanent presence.

The beekeepers were exploring a special trap used in Japan that was placed in front of a beehive, designed to catch an Asian giant hornet before it marks the hive with a pheromone. Tim Lawrence, a professor of entomology at Washington State University with expertise in honeybees, said that in Japan, however, there were smaller beekeeping operations compared with in the United States. In America, he said, it is not uncommon to find hundreds of bee hives in an apiary. “We don’t know what’s going to happen if the hornet is established in an apiary of that size,” Mr. Lawrence said.


Regular beekeeping suits can't protect a beekeeper from the long stinger of the Asian giant hornet either.


Adaptation

While the Asian giant hornet massacres honeybees in their hives, some bees have developed a remarkable defense: cooking the hornets alive.

When a hornet enters the hive of Japanese honeybees, researchers have witnessed how hundreds of bees can respond by forming a ball around a hornet. While the bees face an immense disadvantage in both size and strength, the bees working in unison can vibrate to produce heat, raising the temperature in the formation, like a tiny oven, to over 115 degrees. Bees can survive the high temperature, but the hornet cannot, and after up to an hour of cooking, the hornet dies.


Video


Sadly, European honeybees, which are the most common pollinator in the United States, don’t appear to have the same instinct. They try to defend against a hornet attack by stinging the invaders, but the Asian giant hornet carries a rigid exoskeleton that makes bee stings ineffective, according to researchers.

“The honeybee in Japan has adapted with this predator and learned through generations to protect themselves,” said Ruthie Danielsen, a beekeeper in Birch Bay, Wash., near where two Asian giant hornets were discovered. “Our honeybees, the predator has never been there before, so they have no defense.”


The Sting

How does it feel to be stung by an Asian giant hornet, Vespa mandarinia? It hurts. A lot.

The sensation is like being “stabbed by a red-hot needle,” says Shunichi Makino, who studies wasps and bees at Japan’s Forestry and Forest Products Research Institute. Not only that, but the anguish lingers.


“Usually, the stung part severely swells and continues aching for a few days,” Makino explains, via email. And “although you could also have these symptoms when stung by the other hornet species, the intensity is said to be much more severe in Vespa mandarinia.”

Soichi Yamane got stung on the job. He was a wasp researcher—now retired—and he confirms Makino’s description: “The pain lasted two days, and my sleep was often disturbed by severe pain.” YouTube personality Coyote Peterson once showed what the sting was like on his wilderness series.


The toxicity of venom from the Asian giant hornet, and from a handful of its close relatives, is considerable. It’s greater than the toxicity of most other stinging insects, says Justin Schmidt, who has studied the hornets. An entomologist at the University of Arizona’s Southwestern Biological Institute, Schmidt is an expert in venom. He developed a well-known scale of sting painfulness, known as the Schmidt pain index.


In a 1986 paper co-authored by Schmidt, Yamane, and others, the researchers took venom from various species of giant hornet and injected it into lab mice, a standard experiment at the time for testing a substance's toxicology.


Researchers determine toxicity using a measure called the LD50. Also known as the median lethal dose, it's the quantity necessary to kill 50 percent of test subjects, usually small animals like mice. In their 1980s research, the scientists found that giant hornet venom has an LD50 of 4.1 milligrams per kilogram—a level similar to other closely related hornets. The less venom required for a lethal dose, the more dangerous the substance. For comparison’s sake, the LD50 of honeybee venom is 2.8 mg/kg. And the world’s most toxic insect venom belongs to the Maricopa harvester ant, with an LD50 value of about 0.1 mg/kg in mice.


Though honeybees have venom that’s more toxic than giant hornets, the bees can sting only once. Giant hornets can sting repeatedly, and are capable of delivering about 10 times more venom. The scientists determined that the venom in one giant hornet would be capable of killing about 10 mice—and that a small colony could kill a 150-pound animal.


It makes sense that the species carries a lot of venom, as it is the world’s largest hornet at more than 1.5 inches long. But even they are not the most militant in defending their nests: Yellow hornets (Vespa simillima) native to Japan may actually be more dangerous given their aggressive behavior yet smaller size, says Seiki Yamane, Soichi’s brother, who also studies wasps, at Kagoshima University Museum.


Keeping Safe

For the venom to reach life-threatening levels, a person likely would have to be stung by a couple hundred giant hornets, Schmidt says, compared with about a thousand honeybees.

In Japan, giant hornets cause between 30 to 50 deaths per year, but most of the fatalities are due to allergic anaphylactic reactions rather than acute toxicity, Schmidt says.


It’s important to remember, however, that giant hornets, like other wasps, generally will not attack unless bothered. Especially when the insects are out foraging, they are likely to ignore humans; most deaths from giant hornets’ stings occur because people seriously disturb the insects' nests.

Schmidt observes that giant hornets do give a warning before they sting: They fly back and forth snapping their mandibles. “That is intimidating, that gets your attention,” Schmidt says. “It’s the only species that does that.”


Schmidt himself has never been stung by an Asian giant hornet, even though he began working with them in 1980. His Japanese colleagues advised Schmidt to put on a thick sweatshirt under his bee suit to thwart the insects’ long stingers. That worked—though Schmidt does sometimes regret it. “In hindsight," he says, "I kind of wish I had been stung because that would be a pertinent data point."


Physical Characteristics

The hornet, which can grow up to two inches long, uses its sizable mandibles to snip the heads off of smaller insects for food. Within the mandible, these insects also have a black tooth that they use to dig underground nests. The hornet's stinger alone is one-quarter inch long, long enough to penetrate regular beekeeping suits. Their venom is so potent, it can dissolve human flesh and can kill a mouse in a few seconds. The queens are the largest of the species, growing to 2 inches long with a 3-inch wingspan. For reference, that's wider than an iPhone X. Worker hornets grow to be 1.4 to 1.6 inches long.


V. mandarinia, the "murder hornet" species, sports yellowish and orangeish stripes on its rear end in images the researchers collected, as well as a black thorax and a distinctive orange face. Found in India, Sri Lanka, Bhutan, Nepal, Myanmar, Thailand, Laos, Vietnam, Malaysia, Malaya, China, Hong Kong, Taiwan, eastern Russia, Korea, Japan — and now the Pacific Northwest — it also has a characteristic tendency to nest underground in mammal burrows and the cavities left behind by decaying plant roots, the researchers reported, "enlarging them as the colony develops."




Life Cycle

The hornet's life cycle begins around April. Queens spend the spring building up their colonies in underground nests. A finished nest is about the size of small human child.


During the spring and early summer months, worker hornets — female hornets that do not reproduce — help new queens, like the one seen here, to maintain the hive and raise the larvae. Meanwhile, adult male hornets hunt alone and bring their plundered insect proteins back to the nest to feed their young.


In the warmer summer months, swarms of Asian giant hornets ambush beehives in groups; this behavior is literally called the "slaughter phase." Finally, once the hornets' insectile coup is complete, they begin the "occupation phase." Hornets stick around in an overthrown beehive for several days, even up to two weeks, feasting on the young bees inside.


Mating season for the Asian giant hornet takes place in the fall. Queens release pheromones to initiate reproductive behavior from male hornets. After fertilization, queens leave the nest to start their own colonies. As with many hornet species, fertilized eggs hatch into female hornets — the next generation's queens and workers. Unfertilized eggs, with just one chromosome set, become male hornets, called drones.


Hungry?

In Japan's central Chubu region, the Asian giant hornet is not just considered a pest. It's also a delicacy.  Adult hornets are fried on skewers and eaten whole — stinger and all. It is said that eating these insects produces a pleasant tingling sensation in the mouth. Live hornets are also drowned in shochu, a Japanese liquor. Before they die, the hornets release their venom into the spirits.


Did I Just See a Murder Hornet?

Unless you live in the Pacific Northwest, it is extremely unlikely that you have spotted a murder hornet near your home, according to experts. And we want to keep it that way - fingers crossed, the entomologists and scientists in the western part of the United States are successful in eradicating this insect before it starts spreading across the United States.


If you are believing that you may have seen a murder hornet, chances are you may have seen one of the following:

  • Cicada killer wasp

  • Paper wasp

  • Yellow jacket wasp

  • Mud dauber wasp


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