Asian Giant Hornets: What comes next?

Nancy has a new project called the SciHive on Facebook, and it’s a great resource if you want to interact with professional entomologists (like us!). In light of the Washington State Department of Agriculture exterminating a Asian Giant Hornet nest, I thought this question was worth a full discussion:

So I just read a newspaper talking about the giant Asian hornets that were caught , and it claims it was a nest of 85? Is that a normal nest size , seems low to me? Not there long enough to increase numbers maybe? Someone who knows wasps educate me please 😊

Eliminating invasive species requires you to act fast and act early, because finding and eliminating a handful of nests is easier than finding and eliminating a lot of nests. So it helps to really understand what the WSDA is up against.

So let’s talk about the nesting biology of V. mandarinia and what the WSDA is potentially anticipating for next season.

Vespid wasps-the family Asian Giant Hornets are a part of-is a hugely diverse family. The nest sizes can range from a single, solitary female (Stenogastrinae, Eumeninae) who makes several nests throughout the season to massive yellowjacket nests which can house more than a quarter-million worker wasps. Paper wasps, which build the umbrella-like nests around your house, make what’s probably the average-sized nest of this family and they typically number a couple dozen. That’s still a pretty big range!

First Asian Giant Hornet nest found in US. Image courtesy of Fox News

The genus Vespa, which includes the Asian Giant hornet builds nests that are on the large size but not overly huge. Vespa crabro, the invasive European hornet found on the east coast, typically builds nests in the ~2-400 worker range.

Vespa mandarinia tends to build fairly large nests, but the nest eliminated by the WSDA was only about 85. This can be affected by many different factors, including the time the nest was founded, the climate, food avaliability during the current and previous seasons, and potentially parasites the queen picks up. I just want to make it clear that we don’t know what the typical nest size is for this species in this country. V. mandarinia builds slightly larger than average nests for this group of wasps. The typical colony is about 200-500 workers, although nests as large as 600 can have recorded.

So, the size of the colony represents the hazard exterminators expose themselves to when taking care of a nest. 200 might not sound like a lot, but this many pissed off wasps is actually pretty dangerous…even with standard beekeeping gear. No matter how experienced an exterminator thinks they are-even if they brand themselves as the “leading expert in stinging insect control”-it’s a really good idea to leave this up to people who understand the biology of these insects.

WSDA employee eliminating V. mandarinia nest. They’re wrapping the nest in plastic, and then drowning the nest in carbon dioxide. The majority of the nest was eliminated, but some workers and future queens returned the next day. Image courtesy of USDA.

In terms of how likely these insects are to establish, it depends on how many workers this nest produced. Again, this can vary based on a lot of factors, but the typical V. mandarinia nest produces between 100 and 400 new queens…so equal to or slightly smaller the amount of workers.

Nests made by social wasps have a tendency to fail. Queens can die in the wild, because they’re kind of vulnerable without an army of workers to protect them. Spiders, birds, mantids, and other predators are more than capable of taking down a queen and mortality tends to be high as a result. Wasps always produce more queens than they need, because they need to outpace natural mortality.

Hornet foundress success rate, courtesy of Archer (2010).

The success rate of nests for Vespa isn’t super well defined, and I couldn’t find super great numbers on this. Vespa crabro, the most closely related was to V. mandarinia in the US, has a success rate of ~25% when building a nest. Even though the total number of observations for V. crabro was low (9 total), the average among this subfamily is roughly on par with this number (30%, based on 304 observations over 15 different papers on 8 different species in this subfamily).

The Bottom Line

I can’t predict the future, and I feel like it would be irresponsible to predict the exact number of queens which were produced with this nest. The nest they found was very small for this species, and likely produced a relatively small number of reproductives. Most queens don’t survive, and approximately 70% of the queens which do survive will not succeed in building nests.

That being said, I do think it’s likely that this nest did produce queens. The queen production season of this species is roughly October-November, and they eliminated this nest in late October. It’s only partway through the queen production season, and they’re not in an optimal environment. It looks like the nest didn’t produce as many queens as it could have.

That being said, there’s no way of knowing how many nests weren’t detected. This could have been the only one, but it’s not impossible there’s a nest foraging in a place where it’s hard to observe. Blaine, WA seems pretty rural. I also have no idea how likely they are to hitch-hike on cars, in hay shipments, or in cross-state commercial shipments.

If you’re living in the Pacific Northwest, you can report sightings here. If you’re outside that region, and want to see if you’ve found one, we definitely reccomend you run the insect by an entomologist to confirm the ID. There’s a number of ways to do this, through Facebook (either on SciHive or The Entomology Group). You can email any entomologist at your local land-grant University. There’s also a VERY active entomology community on Twitter (AaE maintains a Twitter account, as do all of our authors) and any one of us can accurately ID an Asian Giant Hornet so please don’t feel like you’re bothering us by asking us for an ID.

Due to the volume of the emails we receive, we typically don’t ID insects…however, in this case, we’re happy to take a look at any suspected AGH and send you to an appropriate place where you can report the insect if the insect is a bona-fide AGH. If it’s not, we probably won’t reply because ID emails take up a lot of our time.

This is a problem which requires a lot of people watching very closely, so keeping an eye out is definitely the best thing we can do. As our audience, we’d really appreciate y’all keeping an eye out for us…even if most of the bugs you find aren’t AGH.

Works Cited

Archer, M. E. (2010). The queen colony phase of vespine wasps (Hymenoptera, Vespidae). Insectes sociaux, 57(2), 133-145.

Archer, M. E. (1994). Taxonomy, distribution and nesting biology of the Vespa bicolor group (Hym., Vespinae). Entomologist’s Monthly Magazine, 130(1560-63), 149-158.

MATSUURA, M., & KOIKE, K. (2002). Studies on the ecology of social wasps and bees in urban environments 1. Records on aerial nests of the giant hornet, Vespa mandarinia japonica (Hymenoptera: Vespidae) within human buildings. Medical Entomology and Zoology, 53(3), 183-186.

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1 Response to Asian Giant Hornets: What comes next?

  1. jonrichfield says:

    Can’t help wondering whether it would be possible to train dogs to sniff out their nests.


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