Sunday, September 12, 2010

Asian giant hornet


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), with a wingspan of about 76 mm (3 in).

Anatomy

The head of the hornet is orange and quite wide in comparison to other hornet species. The compound eyesocelli 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). and
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.



Geographic distribution


It can be found in the Primorsky Krai region of Russia, Korea, China, Taiwan (where it is called  "tiger head bee"), Indochina, Nepal, India, and Sri Lanka, but is most common in mountainous areas of Japan.



Sting



The stinger of the Asian giant hornet is about 6 mm (¼ in) in length, and injects an especially potent venomcytolytic 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 his leg." that contains, like many bee and wasp venoms, a
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[6] 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 exceeds that of all other venomous and non-venomous wild animals combined, including wild bears and venomous snakes.
A few interesting notes on Vespa mandarinia's venom and stinger:
  • The venom contains at least eight distinct chemicals, some of which damage tissue, some of which cause pain, and at least one which has an odor that attracts more hornets to the victim.
  • The venom contains 5% acetylcholine, a greater concentration than is present in bee or other wasp venoms. Acetylcholine stimulates the pain nerve fibers, intensifying the pain of the sting.
  • Vespa mandarinia uses its large crushing mandibles, rather than its sting, to kill prey.
  • The venom of the Asian giant hornet is not as toxic as some other bees or wasps, and is less toxic than honeybee venom, but because of the large quantity of venom, this species has one of the greatest toxicities per sting.
  • The enzyme in the venom is so strong that it can dissolve human tissue. On some occasions, the sting may be compared to the effects of a spider bite.
  • Like all hornets, V. mandarinia has a barbless stinger, allowing it to sting repeatedly

 

 

Predation

The Asian giant hornet is a relentless hunter that preys on other large insects such as bees, other hornet species, and mantises.
The hornets often attack honey bee hives with the goal of obtaining the honey bee larvae. A single scout, sometimes two or three, will cautiously approach the nest, giving off pheromones which will lead the other hornets to the hive's location.
The hornets can devastate a colony of honey bees: a single hornet can kill as many as 40 honey bees per minute thanks to their large mandibles which can quickly strike and decapitate a bee. It takes only a few of these hornets a few hours to exterminate the population of a 30,000-member hive, leaving a trail of severed insect heads and limbs. The European honey bees Apis mellifera have small stings which do little damage to hornets that are five times their size and twenty times their weight. The honeybees make futile solo attacks without mounting a collective defense, and are easily killed individually by the hornets. Once a hive is emptied of all defending bees, the hornets feed on the honey and carry the larvae back to feed to their own larvae. The hornets can fly up to 60 miles (97 km) in a single day, at speeds of up to 25 miles per hour (40 km/h)
Adult hornets cannot digest solid protein, so the hornets do not eat their prey, but chew them into a paste and feed them to their larvae. The larvae produce a clear liquid, vespa amino acid mixture, which the adults consume; larvae of social Vespidae produce these secretions, the exact amino acid composition varying considerably among species. The passing of nutrition to adult wasps by larvae is widespread in these wasps, and not restricted to the genus Vespa.


Native honey bees


Although a handful of Asian giant hornets can easily defeat the defences of many individual honeybees, whose small stings cannot inflict much damage against such a large predator, the Japanese honey bee (Apis cerana japonica) possesses a collective defence against them.
When a hornet scout locates and approaches a Japanese honey bee hive it will emit specific pheromonal hunting signals. When the honeybees detect these pheromones, a hundred or so will gather near the entrance of the nest and set up a trap, keeping it open apparently to draw the hornet further into the hive or allow it to enter on its own. As the hornet enters the nest, a large mob of about five hundred honey bees surrounds it, completely covering it and preventing it from moving, and begin quickly vibrating their flight muscles. This has the effect of raising the temperature of the honey bee mass to 47 °C (117 °F). The honeybees can tolerate this temperature, but the hornet cannot survive more than 46 °C (115 °F), so it dies. Often several bees perish along with the intruder, but the death of the hornet scout prevents it from summoning reinforcements, which would wipe out the colony. More recent research indicates, however, that while the raised temperature of the bee ball contributes to the death of the hornet, it alone is not sufficient to kill the hornet. The bee balls also produce a much higher level of carbon dioxide, which contributes to the hornet's death, although whether this is because it reduces the hornet's tolerance for high temperatures or actually suffocates it, is not known.
Beekeepers in Japan attempted to introduce the European honeybee in order to increase productivity. European honeybees, however, have no defence against the hornet and these formidable insects rapidly destroy the colonies.


Predators

The giant Asian hornet has very few natural predators. The Honey Buzzard  is known to attack hornet nests in groups. No insect in the hornet's area has the capacity to be a threat to the hornet. The only danger that the hornet faces comes from humans. Some villages in Japan value these creatures as part of a human diet. They are eaten either as hornet sashimi or deep-fried. Despite the risks associated with the capture of hornets, they are said to be delicious and a good source of protein.


Hornet supplement manufacturers

Recently, 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 supplement rather than pharmaceuticals, they do not have to support their claims. Some studies, however, have suggested that the vespa amino acid mixture itself may influence animal performance in minor ways.
One such company is Meiji Milk Products Co. of Japan, which manufactures several such hornet-themed supplements under the VAAM brand. According to the products' nutritional information, these all consist mostly of common amino acids and flavourings.

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