How did the Asian giant hornet make it to the US? This social species makes medium sized colonies (~ 300 workers). In the Spring, single mated queens lay eggs that emerge into larvae that they initially rear alone until workers emerge and start helping out. Washington State Department of Health guidelines for Asian giant hornets states that “Queens [of Asian giant hornets] mainly overwinter alone in chambers that they excavate in soil, but they have also been found overwintering in rotting logs and straw”.[…] Researchers think that international cargo containing pots for bonsai trees was responsible for the introduction of a similar species, Vespa velutina, into Europe.” However, it is also possible live nests may have been purposely imported since fried or otherwise prepared larvae are considered a delicatessen by some. Nests of Vespa mandarinia can fetch high prices in Asia.
Does the 2020 detection of two Asian giant hornets queens mean the species is established in the US? The likelihood they will become established will depend on their ability to develop successful nests now. A full colony was destroyed near Nanaimo, Canada in 2019 and no others were detected. However, (A) the 2019 specimens from Canada (Intro#1) had a different genetic signature than those collected in Washington state (Intro#2) (WSDA, unpublished data); (B) the two queens found in May 2020 were in the general vicinity of the US (Intro#2) infestation, which indicates that a colony big enough to generate several queens was present in that area (on the Canadian or US side) in 2019.
How bad it it that Asian giant hornets survived the winter in Washington State or in Canada? This strong predator can decimate colonies of European honeybees (another exotic, that, however, works for us). Of note, in the eastern US we already have an invasive hornet – Vespa crabro, the European hornet (https://en.wikipedia.org/wiki/European_hornet), brought in the mid 1800s by European settlers most likely not on purpose. The European hornet also attacks honeybees although its impact has been limited, maybe because it is not very abundant. It is smaller than the Asian giant hornet (but still significant, at 1 inch or so) and they too can be strong fliers. However, it never made it to the West coast.
Importantly, in social insects like hornets, workers are sterile and unable to start an infestation if moved far. Big invasive jumps are relatively rare and almost without exception associated with human movement. In hornets only a fertilized queen (or a complete hive) is able to start a new colony.
The Asian giant hornet is on the USDA-APHIS list of quarantine species and has been intercepted at ports of entry in cargo.
Click here to be taken to a page with Asian giant hornet lookalikes, especially those in the northeastern US.
Photo credits: the Washington State Department of Agriculture
Fonseca Lab 