Genus: Vespa Linnaeus, 1758
Species: Vespa mandarinia Smith, 1852
Common names: Asian giant hornet (suggested common name), Japanese giant hornet, Yak-killer hornet, Suzumebachi (sparrow wasp in Japanese)
Vespa mandarinia Smith is one of the world’s largest hornets. Commonly referred to as the Asian giant hornet (AGH), V. mandarinia’s size and distinctive markings make it relatively easy to distinguish from other Hymenoptera. Vespa mandarinia is native to eastern Asia, and it is considered one of the most important threats to European honey bees because thousands of managed beehives of Apis mellifera are destroyed by this species every year. This species also poses a public health risk; several people are killed each year by V. mandarinia in its native range. Asian giant hornets are used in food and traditional medicine throughout Asia. The larvae and pupae are eaten as a seasonal delicacy, and adults are fermented to produce a special hornet liquor. Vespa mandarinia was first found in North America in mid-August 2019 in the Nanaimo Area of Vancouver Island, Canada. It was first reported in the U.S. when a dead hornet was found near Blaine, Washington in December 2019.
Vespa mandarinia is native to East Asia, where it has been recorded from Bhutan, China, northern India, Japan, Korea, Laos, Malaysia, Myanmar, Nepal, the Russian Far East, Taiwan, and Thailand. In North America, it has been found in far northwestern Washington (Whatcom County) and southwestern British Columbia (Vancouver Island and near Langley/Abbotsford). As of May 2021, V. mandarinia has not been discovered anywhere else in North America.
Vespa mandarinia can be distinguished from most other large hornets by its distinctive size; large, yellow to orange head with dark eyes; and distinctively cleft clypeus. Vespa crabro, the European hornet, is the only Vespa species established in North America, and it is easily distinguished from V. mandarinia by head characters and general coloration. Vespa mandarinia most closely resembles V. soror and V. analis, two co-occurring Asian species that can appear very similar; keys to species in Nguyen et al. (2006) and Smith-Pardo et al. (2020) can be used to separate these taxa.
Body length: Workers are 25 to 40 mm long, and queens can exceed 45 mm in length. Worker body size increases through the season as the nest grows larger. In late summer and in fall, the overlap in size between large workers and new queens can make caste determination difficult (Matsuura and Koike 2002). Drones (males) resemble females but have one more antennal segment (13 total), one more visible metasomal segment, and lack a sting.
Coloration: The head is large and entirely yellow or orange with dark eyes; the thorax is mostly dark brown or black, making a striking contrast with the head color; and the abdomen usually has alternating bands of dark brown or black and yellow or orange. Vespa mandarinia’s color varies geographically, which has led to description of numerous synonyms, subspecies, and varieties, including: bellona, japonica, latilineata, magnifica, nobilis, and sonani (Carpenter and Kojima 1997; Nguyen et al. 2006; van der Vecht 1959). A few color forms appear to be geographically restricted (Archer 1995), although the taxonomic importance of these color forms is unclear.
Early in the season, dispersing queens feed on fermented tree sap and other plant secretions. Once the nest is established, workers seek out other arthropods, such as scarab and longhorn beetles (Matsuura 1988), mantids (Matsuura 1984), caterpillars and spiders (Matsuura and Sakagami 1973), and other Hymenoptera to feed to the developing brood. For much of the year they are solitary hunters, but late in the season, when males and new queens are developing, multiple hornets will participate in mass attacks on nests of other social Hymenoptera, such as yellowjackets (Vespula), paper wasps (Polistes), and honey bees (Apis) (Lee 2010; Matsuura and Sakagami 1973). Vespa mandarinia usually target nests that are within one kilometer of their own nest (Matsuura and Sakagami 1973).
Vespa mandarinia are social hornets, with annual colonies in temperate zones and perennial colonies in tropical zones (e.g., Thailand). Adult females are divided into two castes: queens that are responsible for starting a colony and laying eggs, and workers that are responsible for gathering food and rearing larvae. Adult queens live nearly a year, whereas adult workers live for 15–35 days (Archer 1995). Developmental time from egg to adult is about 40 days. Approximate time for each stage is: egg, 6 days; larva, 16 days; and pupa, 18 days (Matsuura 1984). The average colony produces around 200 males and new queens (Archer 1995). One of the largest nests found contained 540 active workers and 4,677 cells, 670 of which were queen cells (Matsuura and Koike 2002). The nest found near Nanaimo, British Columbia in 2019 had approximately 200 cells. The nest found near Blaine, Washington in 2020 had approximately 776 cells and contained 9 drones and up to 184 queens (many of the capped pupal cells were assumed to be queen cells based on their size). Vespa mandarinia fiercely defend their nests (Lee 2010) but do not attack people unless threatened.
The following is a descrption of the life cycle of V. mandarinia in a temperate zone (with annual colonies). A fertilized queen emerges from overwintering in the spring (approximately April) and looks for a suitable nesting site. Preferred nesting sites are pre-existing underground cavities such as rodent burrows, under overhangs, in tree roots, and similar habitats. As the colony grows, workers increase the size of the cavity and deposit soil pellets near the entrance, which can aid in locating nests (Lee 2010). However, nests have been occasionally observed in hollow trunks or roots of dead trees (Matsuura and Koike 2002). The nest found near Blaine, Washington in 2020 was located in a hollow tree approximately 8 feet off the ground.
Once the queen finds a suitable site, she alone starts building the nest, foraging, laying eggs, and caring for her young. When about 40 workers are in the nest, the queen becomes completely nest-bound, and the workers assume all duties for the colony except for egg laying (Matsuura and Sakagami 1973). Throughout the summer, the queen produces hundreds or thousands of sterile worker hornets. In late summer through fall, the queen lays tens or even hundreds of eggs (depending on resources and colony size) that hatch into males (unfertilized eggs) and new queens (fertilized eggs) to produce next summer’s generation. To obtain sufficient food for these new reproductives, V. mandarinia may attack honey bee hives and the nests of other social wasps, taking the larvae and pupae back to their nest to feed the developing brood.
In late fall, the males and new queens leave the nest, mate, and disperse. New queens that mate successfully disperse to overwinter in shelters that are constructed in the soil, in cavities of trees, and in abandoned nests of other hornets. The original queen, all of her workers, and the males die before the onset of winter (Matsuura 1984). A single queen can produce up to 200 new queens, although not all of these new queens will mate, survive the winter, and find a suitable nesting site to start new colonies the following spring.
Outside of Asia, V. mandarinia has been introduced to northwestern Washington and southwestern British Columbia in North America. Reports of V. mandarinia in Europe likely refer to V. velutina, which is sometimes called the "Asian hornet."