Japanese giant hornet

Japanese giant hornet
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Vespidae
Genus:	Vespa
Species:	Vespa mandarinia
Subspecies:	V. mandarinia japonica

The Japanese giant hornet (Vespa mandarinia japonica) is a subspecies of the world's largest hornet,^[1] the Asian giant hornet (V. mandarinia). It is a large insect and adults can be more than 4.5 centimetres (1.8 in) long, with a wingspan greater than 6 centimetres (2.4 in). It has a large yellow head with large eyes, and a dark brown thorax with an abdomen banded in brown and yellow. The Japanese giant hornet has three small, simple eyes on the top of the head between the two large compound eyes. As the name implies, it is endemic to the Japanese islands, where it prefers rural areas where it can find trees to nest in. ^[2] In Japanese it is known as the ōsuzumebachi (おおすずめばち（大雀蜂、大胡蜂）, literally "giant sparrow bee").

Description

Japanese giant hornet

Workers forage to feed their siblings. Their diet consists of a wide range of insects, including crop pests, and for this reason the hornets are regarded as beneficial. The workers dismember the bodies of their prey to return only the most nutrient-rich body parts, such as flight muscles, to the nest. There, the workers chew the prey into a paste before feeding the larvae which in return produce a fluid consumed by the workers. This fluid is known as vespa amino acid mixture (VAAM). Synthetic VAAM is being produced artificially as a dietary supplement, with claims that it can increase athletic performance. In many Japanese mountain villages, the hornet is considered a delicacy when fried.^[2]

Bee predation

In Japan, beekeepers often prefer European honey bees because they are more productive than the endemic Japanese honey bees. However, it is quite difficult to maintain a captive hive of European honey bees, as the giant hornets are devastating to the bee hives. Once a Japanese giant hornet has located a hive of European honey bees it leaves pheromone markers around it that quickly attract nest-mates to converge on the hive. An individual hornet can kill forty European honey bees in a single minute; a group of 30 hornets can destroy an entire hive containing 30,000 bees in a little more than three hours. The hornets kill and dismember the bees, returning to their nest with the bee thoraxes, which they feed to their larvae, leaving heads and limbs behind. The honey and bee larvae are also taken to feed the hornet larvae.

Unlike their European relatives, the Japanese honey bee has a defense against these attacks. When a hornet approaches the hive to release pheromones, the bee workers will retreat back to the hive, leaving an opening to allow the hornet scout to enter. At a given point, the bees emerge from their hiding places in an angry cloud formation containing some 500 individuals.^[2] They form a tight ball around the hornet that acts like a convection oven: the bees vibrate their wings, generating heat via muscular exertion, and then direct the air warmed around them into the inside of the ball. This causes the interior temperature of the ball to rise to 47 °C (117 °F). While significant, this high temperature alone is not sufficient to kill the hornet trapped in the bee ball. However the bees' activity also increases carbon dioxide concentration inside the ball. The hornet's ability to withstand heat decreases as carbon dioxide concentrations increase.^[3] So the 47 °C (117 °F) temperature becomes lethal to the hornets. Meanwhile, the honey bees can withstand temperatures of 48–50 °C (118–122 °F) under the same conditions, so the hornet is killed and the bees survive.

Venom

The Japanese giant hornet is large and can be very aggressive if provoked. It has a venom which is injected by the 6.25 mm-long stinger and attacks the nervous system and damages tissues of its victims.^[2] Tests with mice find the venom not to be the most lethal, having an LD₅₀ of 4.0 mg/kg, which compares to the deadliest wasp venom (to mice) by weight of Vespa luctuosa at 1.6 mg/kg. The potency of the sting is due to the relatively large amount of venom injected.^[4] Being stung is extremely painful and can require hospitalization. Asian giant hornet stings can cause anaphylactic shock in allergic people, and can still be lethal to people who are not allergic, provided 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.^[5] Thirty to forty people die in Japan every year after having been stung.^[2][6]

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