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). The Japanese name for this insect is suzume bachi, literally "sparrow hornet".
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.
It can be found in the Primorsky Krai region of Russia, Korea, 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[disambiguation needed] 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."
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 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 deadly by weight as some other bees or wasps (Vespa luctuosa has the most deadly wasp venom by weight), and is less toxic than honey-bee 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.
- Specific to some wasps, and due in part to its large mandibles, the Asian giant hornet can simultaneously bite and sting, leading to compounded excruciating pain.
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 its 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 honey bees 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 100 kilometres (62 mi) in a single day, at speeds of up to 40 kilometres per hour (25 mph)
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 defenses of many individual honey bees, whose small stings cannot inflict much damage against such a large predator, the Japanese honey bee (Apis cerana japonica) possesses a collective defense against them.
When a hornet scout locates and approaches a Japanese honey bee hive it will emit specific pheromonal hunting signals. When the honey bees 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 the bees begin to quickly vibrate their flight muscles. This has the effect of raising the temperature of the honey bee mass to 46 °C (115 °F). In addition, the mob of honey bees raises the level of carbon-dioxide, around the hornet. At that concentration of CO2, the honey bees can tolerate up to 50 °C (122 °F), 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.
Beekeepers in Japan attempted to introduce the European honeybee in order to increase productivity. European honeybees, however, have no natural defense against the hornet and the colonies are rapidly destroyed.
The giant Asian hornet has very few natural predators. The Oriental Honey Buzzard (蜂鷹) 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.
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