Asian hornet
The Asian hornet, also known as the yellow-legged hornet or Asian predatory wasp, is a species of hornet indigenous to Southeast Asia.
It is of concern as an invasive species in some other countries.
Appearance
Vespa velutina is slightly smaller than the European hornet. Typically, queens are 30 mm in length, and males about 24 mm. Workers measure about 20 mm in length. The species has distinctive yellow tarsi. The thorax is a velvety brown or black with a brown abdomen. Each abdominal segment has a narrow posterior yellow border, except for the fourth segment, which is orange. The head is black and the face yellow. Regional forms vary sufficiently in color to cause difficulties in classification, and several subspecies have been variously identified and ultimately rejected; while a history of recognizing subspecies within many of the Vespa hornets exists, including V. velutina, the most recent taxonomic revision of the genus treats all subspecific names in the genus Vespa as synonyms, effectively relegating them to no more than informal names for regional color forms. The color form causing concern about its invasiveness in Europe has been referred to as V. v. nigrithorax, though this name no longer has any taxonomic standing.Biology
Like other hornets, V. velutina builds nests that may house colonies of several thousand individuals. Females in the colony are armed with formidable stingers with which they defend their nests and kill their prey. The nest is of paper, roughly in the shape of a huge egg, usually at least half a meter long. Unlike the nest of the European hornet, its exit is usually lateral rather than at the bottom. The nesting season is long, and a colony commonly begins by building a nest in a low shrub, then abandoning it after some months and rapidly building a new one high in a tree, possibly as an antiparasitic measure. The next generation of young queens disperses in the late autumn to hibernate over winter.V. velutina opportunistically hunts a very wide range of insects, including flies, dragonflies, and Orthoptera, typically capturing them by pursuit. The major concern about their invasiveness, however, is that when they find a honey bee colony or an apiary, they tend to settle down and specialize in honey bees as their prey, as do the larger Japanese giant hornets. A hornet occupies a position above a beehive as its hunting territory. It flies about within an area of about half a square metre, scanning the direction from which foraging honey bees return to the hive. Each hornet vigorously defends its hunting territory, chasing off any rivals. However, as soon as it catches a bee, it flies off and another hornet replaces it, usually within a few seconds. The circadian activities of the two species of honey bees are similar, and the hunting hornets match them; their most intense activity is in the morning and afternoon, not near dusk or noon.
In its native range, V. velutina mainly hunts Apis cerana, the eastern honey bee, which has evolved a strategy of avoiding hovering hornets by rapid entry and exit from the hive when hornets are about. The guard bees also ball hornets to death. However, where A. mellifera, the western honey bee, has been imported, V. velutina finds them easier prey than A. cerana, because A. mellifera has not been subjected to selection for countering concentrated hawking by hornets. For example, A. mellifera approach their hives more indirectly and slowly when they detect hawking hornets, instead of darting in as fast as possible in the way that A. cerana does. They also ball hornets, but less effectively, and they do not achieve as high a temperature in the ball. Furthermore, when they detect that hornets are hawking, A. cerana tend to withdraw into the nest, but A. mellifera do not.
A. cerana guard bees also use wing shimmering in response to the presence of V. velutina. This is a very generalized response to disturbance and has variously been suggested to be an aposematic signal or a strategy for disruption of visual patterns, similar to the behavior of Apis cerana nuluensis and Apis dorsata. A. mellifera exhibits no such behavior. In any event, when A. mellifera occurs together with A. cerana, V. velutina preferentially hawks A. mellifera foragers.
Distribution
V. velutina originates from Southeast Asia, particularly the tropical regions, from northern India, Pakistan, Afghanistan, Bhutan, China, Taiwan, Burma, Thailand, Laos, Vietnam, Malaysia, the Indo-Chinese peninsula, and surrounding archipelagoes.As an invader, the Asian hornet has appeared in France, Spain, Portugal, South Korea, and Japan. Further invasions are expected in various countries, including much of Europe. A nest was reported on the Channel Island of Alderney in 2016. The first sighting on the UK mainland was announced on 20 September 2016 and occurred near Tetbury in Gloucestershire; the nest was found and destroyed and no breeding adults were found within.
Pest status and invasiveness
V. velutina has become an invasive species in France, where it is believed to have arrived in boxes of pottery from China in 2004. Humans have been attacked after disturbing hornets; although the species is not aggressive, it "charges in a group as soon as it feels its nest is threatened". People have been hospitalised in France after suffering anaphylactic shock as a result of multiple stings. Because of Asian hornets' larger size, their stings are more serious than those of western honey bees. By 2009, several thousand nests were in the area of Bordeaux and surrounding departments, and by the end of 2015, they were reported over most of France.The Asian hornet spread to northern Spain, as confirmed in 2010 by the Beekeepers' Association of the Basque Country and the Neiker entomology institute in Irún, after breeding colonies were found. It reached Portugal in 2011.
El País newspaper carried an article in its October 6, 2013, edition that the Asian hornet had been spotted in Vall d'en Bas, Garrotxa, Catalonia, in the foothills of the Pyrenees. Efforts were made to locate the nests before the insects hibernated in November. After foot patrols failed to track the hornets down, a helicopter equipped with a thermal camera was making sweeps over the area. The flights during the morning chill attempted to find the nest's 'heat signature' against the colder background. In September 2013, a beekeeper from Rasines, Cantabria, documented the hornets' presence in two specimens. In June 2015, firemen pulled a nest of the hornet above a building entrance in Santander. In November 2017, a man was killed in Galicia after being stung over 20 times while pruning an apple tree.
It was reported in Liguria, Italy, since 2012. According to Italian Beekepers' Association in 2017, the Asian hornet was well established in northwestern regions of Italy, and colonization is steadily advancing.
As of October 2017, the species was reported in Belgium.
The Asian hornet has been reported as naturalised on the Japanese island of Tsushima since about 2010.