What are Asian Giant Hornets?
Asian Giant Hornets (Vespa mandarinia) are very large wasps in the family Vespidae, which includes yellowjackets, bald-faced hornets, and paper wasps. They are native to eastern Asia and its outlying islands, notably Japan.
Where are they now?
In the USA, we currently have only found them in a small corner of Washington. If you aren't in Whatcom County, Washington, then it is exceedingly unlikely that you have these in your area.
How did they get here?
We don't 100% know how they got here. The wasps have been found in Blaine, WA, a small border town just south of Vancouver, Canada. One possible scenario is that they flew across the border to the USA from Canada. Asian Giant Hornets have been discovered on Vancouver Island, across the Strait of Georgia from the city of Vancouver. They may also have come directly to the USA, but this is less likely because Blaine, WA is not a cargo destination.
Wasp Biology 101:
Wasps are eusocial insects, which means that they live together as a group with a single queen and several to many female workers. After rearing an initial brood of workers, the queen lays eggs and stays at the nest; the workers tend larvae and venture forth in search of food.
Immature wasps are pale, almost featureless, larvae. Like a caterpillar turning into a butterfly, a larva will pupate into an adult wasp. Because insects only have functional wings as adults, all the wasps you see flying around are fully mature. Insects have an exoskeleton, a hard outer covering that functions as both skin and bones, so adult insects cannot grow larger. This means that if you see small wasps flying around, they will not grow any larger; they have reached their maximum size.
All of the workers are sterile females. This matters, because the stinger is a modified ovipositor (egg laying tube) that can deliver venom. (Venom is poison that is injected via fangs, spines, stingers, etc.). Bees have barbed stingers that tear away from the body to keep pumping venom when the bee stings. Wasp stingers do not; wasps can sting you over and over.
Lifecycle of Asian Giant Hornets:
In the spring, the queen Asian Giant Hornets begin their nests. They build underground nests, never in trees, eaves, or other above ground places. It is a hole in the ground with gigantic wasps flying in and out. To feed themselves and rear the first brood of workers, they seek tree sap. Oak is preferred, but other sap works well too. In Japan, this happens in late April/early May, but it would not be surprising if this adjusts a month in either direction to adapt to local conditions in the USA. The first brood will be smaller workers than ones that emerge later.
As the colony increases, it begins seeking protein in the form of insect prey. It is during this period that the Asian Giant Hornet can destroy a colony of bees. Bee larvae are an excellent protein source, but the adults defend them fiercely. However, Asian Giant Hornets are tough enough that the bees cannot easily harm them. Several dozen of these hornets can eliminate tens of thousands of bees over the course of a few hours. The adult bees are slain and left in broken piles below the hive. Once the slaughter is complete, the hornets take first the pupae, then the larvae, and lastly chew the dead adult bees (and any of their own fallen!) into balls of meat to bring back to their own nest.
Asian Giant Hornet colonies reach their maximum size in late summer, topping out at about 100 workers. In early fall, they stop producing workers and switch to producing only reproductive males and females (i.e. queens). The males fly to other nests to mate and die after a short time. After mating, the new queens overwinter in a small chamber they dig in the soil. The cycle begins again the next year.
Danger to Humans:
These are some particularly nasty wasps. Their large size means that they inject a proportionally larger amount of venom than other wasps. A single sting can be incredibly painful, but no threat to most people. Wasp allergies or particularly unfortunate stings still require medical attention. If someone stumbles on a colony and gets ten to fifty stings, especially from the larger mid-summer workers, it is necessary to seek medical attention.
If you find a nest, avoid it and call a professional. If you are attacked, run and don't fight. These wasps are tough and a slap may not kill them. Even a stomp into soft earth might be ineffective. They are defending and not attacking, so they will stop chasing you once you are far enough away.
Identifying Asian Giant Hornets:
Asian Giant Hornets are huge wasps with an all-yellow or orange head. If you aren't in Washington, you almost certainly won't see one. If you are on the East Coast and think you see one, it is worth looking up the European Hornet before you sound the alarm. If you are very sure that you see one, take a picture on your phone (including that big ol' head), double check with WSDA's website, and send it to either your local department of agriculture, university extension, or the United States Department of Agriculture's Animal and Plant Health Inspection Service (USDA APHIS). Any of these sources will be able to help you.
If you want to send in a specimen, you'll send it to the same sources. To preserve a specimen, either freeze it immediately in the freezer or preserve it in 70% alcohol. (90% alcohol will work too, but may stiffen the specimen.)
About the name "Murder Hornets"...
This name did not exist before New York Times picked the most dramatic translation of a Japanese common name it could find to label Asian Giant Hornets. The majority of entomologists consider the name to be silly and bombastic. For many years, the English name of Vespa mandarinia has been Asian Giant Hornets. Insidiously though, this name also cheapens the word "murder" which is the killing of a person by a person. It is a deliberate blurring of ethical lines via language.
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Stephen Young is an entomologist both in his career of identifying insects for the USDA and in his hobby, insect collecting. He is a Christian, husband, father, and mentor. His opinions are his own and do not necessarily represent those of the USDA.