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Asian giant hornetThe Asian giant hornet (Vespa mandarinia), including the subspecies Japanese giant hornet (Vespa mandarinia japonica), colloquially known as the yak-killer hornet, is the world's largest hornet, native to temperate and tropical Eastern Asia. Its body length is approximately 50 mm (2 in), its wingspan about 76 mm (3 in), and it has a 6 mm (0.2 in) sting which injects a large amount of potent venom.
The head of the hornet is orange and quite wide in comparison to other hornet species. The compound eyes and ocelli are dark brown, and the antennae are dark brown with orange scapes. The clypeus (the shield-like plate on the front of the head) is orange and coarsely punctured; the posterior side of the clypeus has narrow, rounded lobes. The mandible is large and orange with a black tooth (inner biting surface) which is used for burrowing.
The thorax and propodeum (the segment which forms the posterior part of the thorax) of the Asian giant hornet has a distinctive golden tint and a large scutellum (a shield-like scale on the thorax) that has a deeply impressed medial line; the postscutellum (the plate behind the scutellum) bulges and overhangs the propodeum. The hornet's forelegs are orange with dark brown tarsi (the distal—furthest down—part of the leg); the midlegs and hindlegs are dark brown. Wings are a dark brownish-gray. The tegulae are brown.
The gaster (the portion of the abdomen behind the thorax–abdomen connection) is dark brown with a white, powdery covering; with narrow yellow bands at the posterior margins of the tergite, the sixth segment is entirely yellow. It is similar in appearance to the established European hornet, Vespa crabro.
The Asian giant hornet
It can be found in the Primorsky Krai region of Russia, Korea (where it is called 장수말벌; "commander bee"), China, Taiwan (where it is called 虎頭蜂; "tiger head bee"), Indochina, Nepal, India, and Sri Lanka, but is most common in rural areas of Japan, where it is called giant sparrow bee (大雀蜂 or オオスズメバチ?).
The stinger of the Asian giant hornet is about 6 mm (¼ in) in length, and injects an especially potent venom that contains, like many bee and wasp venoms, a cytolytic peptide (specifically, a mastoparan) that can damage tissue by stimulating phospholipase action, in addition to its own intrinsic phospholipase. Masato Ono, an entomologist at Tamagawa University near Tokyo, described the sensation as feeling "like a hot nail being driven into my leg".
An allergic human stung by the giant hornet may die from an allergic reaction to the venom, but the venom contains a neurotoxin called mandaratoxin (MDTX), a single-chain polypeptide with a molecular weight of approximately 20,000 u, which can be lethal even to people who are not allergic if the dose is sufficient. Each year in Japan, the human death toll caused by Asian giant hornet stings is around 30-40.
The Asian giant hornet is intensely predatory; it hunts medium- to large-sized insects, such as bees, other hornet species, and mantises.
An Asian giant hornet feeding on a mantis.
The hornets often attack hives to obtain the honey bee larvae as food for their own larvae. A single scout, sometimes two or three, will cautiously approach the hive, producing pheromones to lead its nest-mates to the hive. The hornets can devastate a colony of honey bees: a single hornet can kill as many as 40 honey bees per minute thanks to its large mandibles which can quickly strike and decapitate a bee. The honeybee stings are ineffective because the hornets are five times the size and too heavily armoured. It takes only relatively few of these hornets (under 50) a few hours to exterminate a colony of tens of thousands of bees. After butchering the bees with impunity, the hornets loot the honey and carry off the bee larvae as food for their own larvae. The hornets can fly up to 100 kilometres (62 mi) in a single day, at speeds of up to 40 km/h (25 mph)
Adult hornets cannot digest solid protein, so the hornets do not eat their prey, but chew them into a paste that they feed to their larvae. The larvae in turn produce a clear liquid, vespa amino acid mixture, which they secrete to feed the adults on demand; larvae of social vespids generally produce these secretions, though the exact amino acid composition varies considerably from species to species. The feeding of adult wasps by larvae occurs generally in predatory social wasps, and not restricted to the genus Vespa.
Native honey bees
A defensive ball of Japanese honey bees (Apis cerana japonica) in which two hornets (Vespa simillima xanthoptera) are engulfed, incapacitated and heated.
Beekeepers in Japan attempted to introduce European honey bees Apis mellifera for the sake of their high productivity. European honeybees, however, have no innate defense against the hornets, which can rapidly destroy their colonies.
Although a handful of Asian giant hornets can easily defeat the uncoordinated defenses of a honey bee colony, the Japanese honey bee (Apis cerana japonica) has evolved an effective strategy. When a hornet scout locates and approaches a Japanese honey bee hive she emits specific pheromonal hunting signals. When the Japanese honey bees detect these pheromones, a hundred or so will gather near the entrance of the nest and set up a trap, keeping the entrance open. This permits the hornet to enter the hive. As the hornet enters, a mob of hundreds of honey bees surrounds it in a ball, completely covering it and preventing it from reacting effectively. The bees violently vibrate their flight muscles in much the same way as they do to heat the hive in cold conditions. This raises the temperature in the ball to the critical temperature of 46 °C (115 °F). In addition, the exertions of the honey bees raise the level of carbon dioxide (CO2) in the ball. At that concentration of CO2, the honey bees can tolerate up to 50 °C (122 °F), but the hornet cannot survive the combination of a temperature of 46 °C (115 °F) and high carbon dioxide level. Some bees do die along with the intruder, much as happens when they attack other intruders with their stings, but by killing the hornet scout they prevent it from summoning reinforcements that would wipe out the entire colony.