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|Asian giant hornet|
|Adults engaging in trophallaxis|
|Asian giant hornet|
|Adults engaging in trophallaxis|
The 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) and its wingspan about 76 mm (3 in), and it has a 6 mm (0.24 in) stinger 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) that is used for burrowing.
The thorax and propodeum (the abdominal segment that is fused with the posterior segment 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.
It can be found in the Primorsky Krai region of Russia, Korea (where it is called 장수말벌; "Commander wasp"), 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.
The venom contains a neurotoxin called mandaratoxin (MDTX), a single-chain polypeptide with a molecular weight of approximately 20 kD, which can be lethal even to people who are not allergic if the dose is sufficient.
Advice in China is that people stung more than 10 times need medical help, and emergency treatment for more than 30 stings. The stings can cause renal failure. Stings by Asian giant hornets killed forty-one people and injured more than 1,600 people in Shaanxi province, China in 2013.
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. The hornets can fly up to 100 kilometres (60 mi) in a single day, at speeds of up to 40 km/h (25 mph)
Hornet larvae, but not adults, can digest solid protein; the adult hornets chew their prey into a paste that they feed to their larvae. Larvae of predatory social vespids generally (not just Vespa) secrete a clear liquid, vespa amino acid mixture, whose exact amino acid composition varies considerably from species to species, which they produce to feed the adults on demand.
Beekeepers in Japan attempted to introduce European honey bees (Apis mellifera) for the sake of their high productivity. European honeybees 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 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 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.
Detailed research suggests that this account of the behaviour of the bees and a few species of hornets is incomplete and that the bees and the predators are developing strategies to avoid expensive and mutually unprofitable conflict. Instead, when bees detect scouting hornets they transmit an "I see you" signal that commonly warns off the predator.
Several companies in Asia and Europe have begun to manufacture dietary supplements and energy drinks which contain synthetic versions of secretions of the larvae of Vespa mandarinia, which the adult hornets usually consume. The manufacturers of these products make claims that consuming the larval hornet secretions (marketed as "hornet juice") will enhance human endurance because of the effect it has on adult hornets' performance. Because these products are marketed as dietary supplements rather than pharmaceuticals, they do not have to support their claims. Some studies have suggested that the vespa amino acid mixture itself may influence animal performance in minor ways.
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