Explanation of Names
Vespa mandarinia Smith, 1852
Queens can exceed 2.0 inches and workers are usually around 1.5 inches long, making them the world’s largest hornet and one of the largest species in Hymenoptera.
Individual wasps have been detected in the Pacific Northwest (nw WA & sw BC), though it is currently not known to be established there. Established is when there is evidence of a reproducing population over multiple years. A single nest was found on Vancouver Island, but was quickly eradicated.
It is native to Japan, but has spread throughout southeast Asia to as far as India and Pakistan - Map (1)
Asian giant hornets typically build their nests underground, usually in abandoned rodent burrows, in forested areas.
Medium to large-size insects, sap and fruit. AGH feed on crop pests, other hornet species or even cannibalize each other's colonies so they are often considered beneficial. Preying mantises tend to be a favorite snack in the late summer and early fall since their large size makes them key protein sources for developing AGH queens and drones. Larvae can digest solid protein; but the adult hornets cannot. They drink the fluids of their prey items, then chew them into a paste to feed to their larvae. The workers dismember the bodies of their prey to carry the most nutrient-rich body parts back to the nest.
Apiarists in North America are concerned since AGH is known to attack honey bee hives, heavily damaging or destroying the colony to feed honey bee larvae to developing AGH larvae. These attacks are also typically in the late summer and early fall, when developing AGH drones and queens need extra protein. In a matter of hours, 15 to 30 AGH can kill a hive of honey bees containing 30,000 to 50,000 workers. It is unknown how the establishment of AGH in North America could affect apiarists and agriculture here.
The nesting cycle of AGH is consisten with other eusocial insects. Queens emerge in early to mid-April and begin feeding on the sap of Quercus (oak) trees. Among the queens there is a dominance hierarchy. The top-ranked queen begins feeding, while the other queens form a circle around her. Once the top queen finishes, the second-highest ranking queen feeds. This process repeats until the last queen feeds.
Mated queens start to search for nesting sites in late April. The unmated queens do not search for nests since their ovaries never fully develop. They continue to feed, but then disappear in early July. A mated queen begins to create relatively small cells in which she raises around 40 small workers. Workers do not begin to work outside of the hive until July. Queens participate in activities outside the hive until mid-July when they stay inside the nest and allow workers to take over outside activities.
Early August marks a fully developed nest, containing three combs holding 500 cells and 100 workers. After mid-September, no more eggs are laid and the focus shifts to caring for larvae. The queens die in late October.
Males and new queens take on their responsibilities in mid-September and mid-October, respectively. During this time, their body color becomes intense and the weight of the queen increases about 20%. Once the males and queen leave the nest, they do not return. Males wait outside the nest entrance until the queen emerges. Once the queen emerges, they intercept her midair, bring her to the ground, and copulate from 8 to 45 seconds. After this episode, the males return to the entrance for a second chance, while the queen leaves. Many queens attempt to fight off the males and leave unfertilized. After this episode, queens hibernate in moist, subterranean habitats until they emerge in April to start the cycle over again.
More detailed information and references can be found in the AGH colony section on wikipedia:
People do not need to worry about the hornet harming them. Their sting is painful, but records indicate the average number of stings that will kill a person is about 60. That many stings usually happen when someone disturbs a nest and the hornets feel threatened. Since there has only been one colony found in North America (which was destroyed), the chances of coming across a nest unexpectedly are very low, especially if you do not live in the Pacific NW or SW Canada.
European honey bees (Apis mellifera) and Japanese honey bees (Apis cerana japonica also have an interesting defense behavior called bee-balling. If an AGH enters a honey bee hive, dozens of workers will cover the hornet (which looks like a ball of bees) and vibrate their wings to heat up their thoracic muscles. As they do this, the bees can produce enough heat to kill the hornet.
It is also important to note the human consumption of AGH. In some areas this species is considered a delicacy, and can be a nutritious protein source.
This is a developing situation and this page will be updated as more information becomes available. People in Washington state should report potential sightings through the Washington State Department of Agriculture website
McGann C. 2019. Pest Alert: Asian giant hornet. Washington State Department of Agriculture.
- Gill et al
., University of Florida, 2020
Tripodi A, Hardin T. 2020. New Pest Response Guidelines. Vespa mandarinia
Asian Giant Hornet. USDA. 62 pp. (Full PDF