Monday, September 13, 2021

Update and repost of Giant Asian Hornet article

See Asian Giant Hornet Fact Guide by James Mason in Virginia Tech’s Department of Entomology for a summary of risk, and an excellent pairing of photos of this species with species likely to be confused.

Fig. 1a, b. Asian giant hornet, Vespa mandarinia, courtesy of USDA-APHIS
Fig. 2. European hornet, Vespa crabro, attacking a blackberry (Pfeiffer)

Hello, everyone, Recently a nest of the Asian giant hornet was found in Washington State, using a new approach to nest detection. Workers are captured and fitted with tracking devices, leading investigators to the nest. I've had some questions about this hornet, and so I'm reposting an article from May 2020. Follow below!

I’d like to say a few words about another invasive insect that has been in the news lately, and is generating questions (I promised myself I would not say generating a lot of buzz, and I’m going to hold to that!). This is the Asian giant hornet, Vespa mandarinia. A recent newspaper article (Baker 2020) used a nickname for this insect – murder hornet - that is a literal translation of a Japanese nickname. One needs to be careful about common names and nicknames of insects. Velvet ants are neither velvet nor ants, but a family of wasps that have been referred to as “cow-killers”, even though they are no threat to cattle. The Asian giant hornet was referred to as a murder hornet to elicit interest in readers, but people have really latched onto it, going beyond mere “elicited interest”! This is the world’s largest hornet, about 45 mm long, about 1.8 inches (queens are larger, about 50 mm, or 2 inches. Their main food consists mainly of insects, e.g. other wasps, beetles and mantises.

Several points need to be made about this wasp: 1) It is nowhere close to Virginia or anywhere else in our region. The discovery was made last December in northwestern Washington State, after being found earlier in the fall in adjacent British Columbia. 2) The known infestation in the US currently consists of two dead wasps found. There was likely a nest that gave rise to these individuals, but it has not been common even where discovered. 3) The US discoveries were across the water from a hive that was discovered in Nanaimo, on Vancouver Island in British Columbia in September. That hive was found and destroyed (Bérubé 2020). A genetic analysis has shown that the wasps from the BC and WA sites were not from the same hive. 4) In Japan about 40-50 people die from stings from this species. In the US from 2014-2017, annual deaths from bee and wasp stings ranged from 43-89 (CDC 2019). 5) The main threat is to honey bees. The wasp workers will attack honey bee hives in order to steal brood. Beekeepers and entomologists in Washington State will be working to find and destroy nests while it is still in a restricted geographical range.

The threat to honey bees: This wasp feeds on a wide range of insects, but in late summer and into the fall will attack honey bee hives. There are several phases of wasp attack against the hive (Matsuura and Sakagami 1973). Early in the cycle, there is a hunting phase, where wasps will wait near hives and attack individual bees as they leave the nest. Later this will progress to a slaughter phase, where groups of wasps will attack worker bees, biting and killing the bees until there is no more defense. This leads to the occupation phase, where bees enter and remove bee pupae to serve as food for the wasp brood. Honey is not taken. During this occupation phase, the wasps become more aggressively defensive and will attack perceived intruders. European honey bees (Apis mellifera) are much more vulnerable than Japanese honey bees (Apis cerana).

You may have read about a response of Japanese honey bees when their hive is threatened by the wasp. I’ll expand on this by including links I have been using in my course on Insect Structure and Function, showing how the insects’ circulatory system is coopted for another use. First – the threat posed to our main honey bee, the European A. mellifera. This bee did not evolve with Asian giant hornet, and so has no effective defense. A scout wasp finds and marks a bee hive, and her nestmates soon arrive to attack the hive. After eliminating the workers, the brood is taken to feed the wasp brood back in their nest. Here is the video depicting the threat to European bees:

The Asian honey bee, A. cerana, has evolved with the hornet, and has evolved a defense – think of this as an evolutionary arms race. When the scout wasp finds the nest, the bees swarm over the invader, vibrate their wing muscles, and generate a heat that heat the blood. This heat is dissipated through the cuticle, or exoskeleton, of the bees. While the temperature generated is tolerable to the bees, it is lethal to the wasp, killing the intruder before her nestmates learn of the hive. Here is the link to a video on that response by A. cerana:

How can Asian giant hornet be managed?: In Japan, several types of approaches to managing Asian giant hornet in bee yards were discussed and summarized by Matsuura and Sakagami (1973) as falling into six categories: 1) Beating to death, 2) Removal of hornet nests, 3) Bait trapping, 4) Mass poisoning, 5) trapping at hive entrances, 6) Protective screens. Many of these were developed on an ad hoc basis by beekeepers and need to be further tested.

Telling Asian giant hornet from wasps that are already here: Because of the widespread public concern over Asian giant hornet, it will be very useful to be able to differentiate that species from insects that may be confused. In addition to size, note the shape of the yellow to yellow-orange head, the yellow stripes on the abdomen (Figs. 1a,b), the dark antennae with yellow-orange scape (first or basal segment), and a wide gena (the area behind the eye). Here is a link to a graphic that compares the Asian giant hornet to several other wasps:

This graphic was developed in Washington State, where the Asian giant hornet was found. Some of the species shown are western species, but we have similar ones here in the east. For example, the yellowjacket shown is Vespula pensylvanica, which, despite its scientific name, is mainly a western species. However, it is similar in size to our eastern species, Vespula vulgaris among others.

Another big wasp, likely to be confused: Because of its large size, the wasp that will most likely be mistaken to be the Asian giant hornet is the European hornet, Vespa crabro. That species was introduced into the US in the middle 1800s, and is now present in much of the east (Akre et al. 1981). It usually not very aggressive, and does not cause the problems that yellowjackets do. This wasp is commonly seen. Note the projections of dark area that cut into the leading edge of yellow striping, a dark area that is somewhat doorknob shaped. This can be seen in the photo (Fig. 2) at the beginning of the post and in the illustration below (Fig. 3).

Fig. 3. Top of gaster (abdomen) of the European hornet, taken from Akre et al. (1981)

See our new fact guide for Asian giant hornet: To help address the public concern, the Entomology Department at Virginia Tech has published a fact guide to the Asian giant hornet (Mason 2020) ( In this article, photos of the Asian giant hornet are paired with photos of several wasps that may cause confusion. Note the differences in size and color pattern. I’ve seen one news article that used the European hornet photo mis-labeled as the Asian giant hornet, creating the potential for further confusion.

In summary, two dead adults of Asian giant hornets were found in Washington State in December, shortly after a nest was found and destroyed in nearby British Columbia. The locality of the originating nest of the US finds is not known, but there is so far no definitive proof that Asian giant hornet is established in this country. The main threat from this wasp is to honey bee hives. Beekeepers are working with the Washington Department of Agriculture and Washington State University to find, and if necessary, work to eradicate this species. It is not expected in the eastern states in the foreseeable future. More important risk to honey bees continues to be parasitic mites and the viruses they transmit, loss of foraging diversity, lack of genetic diversity, pesticides, and overwork!

More later,


References for added enjoyment!

Akre, R. D., A. Greene, J. F. MacDonald, P. J. Landolt, and H. G. Davis. 1981. The Yellowjackets of America North of Mexico. U. S. Dept. Agric. Handbook 552: 102 p.

Baker, M. 2020. 'Murder hornets' in the U.S.: The rush to stop the Asian giant hornet. The New York TImes.

Bérubé, C. 2020. Giant alien insect invasion averted - Canadian beekeepers thwart apicultural disaster. Am. Bee J. 160: 209-214.

CDC. 2019. QuickStats: Number of deaths from hornet, wasp, and bee stings, among males and females — National Vital Statistics System, United States, 2000–2017. MMWR Morb. Mortal. Wkly. Rep. 68 649.

Mason, J. 2020. Asian giant hornet fact guide, Department of Entomology News.

Matsuura, M., and S. F. Sakagami. 1973. A bionomic sketch of the giant hornet, Vespa mandarinia, a serious pest for Japanese apiculture. J. Fac. Sci. Hokkaido Univ. Ser 6, Zool. 19: 125-162.

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