How British Columbia and Washington state are stopping the spread of Asian giant hornets
by Spencer K. Monckton, PhD Candidate, Biology, York University, Canada
Giant hornets are top-of-mind for agricultural authorities in Washington state and B.C.
Panic-stricken headlines about “murder hornets” are thankfully mostly behind us. The nickname may have staying power, but it is certainly unearned.
First spotted in British Columbia in August 2019, the Asian giant hornet (Vespa mandarinia) poses little threat to humans. In its native range in East Asia, the giant hornet is chiefly a menace to the livelihoods of beekeepers, provoking concern that it could cause similar problems in North America.
As a result, giant hornets are still very much top-of-mind for agricultural authorities in Washington state and British Columbia: this spring, the species has turned up again in both places.
Introduced but not established
The three hornets found this spring have all been mated queens, which means at least one colony successfully reproduced last year. Despite that fact, giant hornets are not considered established in North America, which would require successful reproduction over multiple generations.
The species has yet to complete its entire life cycle here; entomologists with the Washington State Department of Agriculture (WSDA), the U.S. Department of Agriculture and the B.C. government are working together to keep it that way.
Through a program of trapping, tracking and removal of giant hornet nests, there is a real chance of reversing this introduction. This is thanks in large part to basic natural history research.
To get out ahead of the giant hornet’s introduction, entomologists are leaning heavily on extensive literature about this species in Japan, where its biology has been studied in exhaustive detail.
Stopping the introduction will in many ways be a race against the clock, but because the giant hornet’s life cycle can be plotted on a calendar, entomologists know just how fast to move and when to act. This is an uncommon advantage when it comes to species introductions and it might make all the difference.
Staying one step ahead
In Japan, giant hornet queens emerge from hibernation in the spring, spending May and June establishing their nests. During this time, the queen lays its first few eggs, which develop into non-reproductive workers. These workers normally emerge in July, taking over the jobs of building and provisioning the nest. After a couple of weeks, the queen shifts focus to laying eggs full-time, and the colony begins to grow in earnest. As colonies grow, workers become more and more common.
Strategies for detection will concentrate on trapping workers beginning in July. As worker hornets show up in traps, entomologists hope to be able to zero in on established nests and destroy them before the summer is out.
In mid-summer, giant hornets are not expected to cause too much trouble. At this stage, they mostly hunt individual insects, including wasps, large beetles and foraging honey bees. It is not until late August to early September that giant hornets undergo a dramatic shift in behaviour and begin attacking honey bee colonies.
An entire honey bee colony can be destroyed in the course of a few hours by a handful of attacking hornets. Although devastating, these attacks are conspicuous, which might make the hornets easier to track. Once this stage of the giant hornet’s life cycle begins, authorities will need to focus their efforts on investigating reported attacks.
Giant hornets occupy defeated bee hives for a few days while they empty the hives of protein-rich bee larvae and pupae. Entomologists may be able to take advantage of this behaviour by staking out hornet-occupied hives and following workers back to their nests. Technologies like miniature tracking tags and heat vision cameras can help locate underground hornet nests.
If that sounds like overkill, consider that attacks on honey bees represent some of the last opportunities to track down established hornet nests. It is unknown why giant hornets suddenly begin attacking honey bee colonies in late summer, but one hypothesis is that it’s due to an increased need for protein in the nest. That protein is needed to support the development of upwards of 300 reproductive females, each of which is a potential future queen.
Males and reproductive females emerge in late October and November, and remain in the nest just long enough to eat all the food they’ll need to mate and, in the case of the females, survive the winter. By the time attacks on honey bees are investigated and confirmed, authorities may only have a few weeks left to stop another generation of queens from being produced.
For that reason, entomologists at the WSDA will be working hard to ensure that as many nests can be located and destroyed as early as possible. Besides placing a large number of their own traps, they are enlisting the help of the public to set out homemade hornet traps, and to report any suspicious sightings using an online form.
The logic is simple: the more workers that are detected, the easier it will be to work out the locations of any established colonies throughout the summer.
At the moment, entomologists are cautiously optimistic, being careful to recognize the gaps in our knowledge. For one, we don’t know how many colonies were able to reproduce before the end of 2019. One colony on Vancouver Island near Nanaimo, B.C., was located and destroyed before any reproductive females were produced, but no colonies were found on the mainland of British Columbia.
We also don’t know just how far founding queens travel before they establish their nests; in other hornet species, this can range from less than one to a few dozen kilometres. The locations of this spring’s queens tell us either that the new queens travelled up to 35 kilometres before founding their nests or that they came from more than one colony. Either way, it probably means that giant hornets could spread faster than initially thought.
On the other hand, any number of factors might work in our favour, such as differences in the climate and ecosystems on the West Coast of North America compared to Japan, or the likelihood that any successful colonies from last year were smaller than average. With any luck, the number of colonies to locate could be as few as two dozen or so. Until hornets start turning up in traps, however, we can only speculate.
It’s not clear how the summer will play out. But thanks to decades of basic research on this remarkable insect, we are well informed and well prepared, and we stand a very real chance of stopping the giant hornet’s introduction.