AKA the Japanese giant hornet, Yak Killer Hornet, Suzumebachi ('sparrow bee'), and Tiger Bee.
Class: Insecta
Order: Hymenoptera
Family: Vespidae
Genus: Vespa
Species: Vespa mandarinia
The Asian Giant Hornet is the largest hornet in the world, at 25-45 mm long for the workers, and up 55 mm for the queens (just over 2 inches). The Japanese subspecies, Vespa mandarinia japonica is also said to have the most venomous sting of all wasps, although this may be due to the volume of venom in a sting rather than its potency; a honeybee's venom actually has a higher LD50, and the strongest venom by weight belongs to Vespa luctuosa.
Asian Hornets live in South-East Russia, throughout South-East Asia, India and Japan. They are the size of a person's thumb, and have yellow and black stripes, with a wide yellow-orange head. They have dark brown wings, and a wingspan of about 76 mm (3 in).
The nest is essentially the same as the nests of other hornets, made of a 'paper' of chewed plant materials (usually the bark of a white cedar) and hornet spit. The Asian giant hornet is unusual in that it prefers to build its nest underground, usually within rotting root cavities or in the burrows of small animals. This doesn't prevent the nests from reaching quite large sizes, and nests larger than basketballs are not uncommon. They will also sometimes build nests in nooks and crannies of urban houses, although this is rare.
They will attack many types of large insects, focusing primarily on beetles such as longhorn beetles and scarabs. They are best known for hunting bees, not because this makes up the major part of their diet, but because when they go after a bee hive they kill all the bees. Once the scouts find a promising nest they release a scent to alert other hornets that there is food to be had. They enter the hive, biting off the heads of all the adult bees. When attacking honey bees, they can kill up to 40 a minute, and devastate the hive in a matter of hours. They drink the bee's honey and carry off the bee larvae to feed their young, leaving the hive dead.
While farmers raising honey bees routinely put out traps for these hornets, the bees also have a defense of their own. The native Japanese honeybee (Apis cerana japonica) will pile themselves onto the invading hornets, hundreds of them at a time. The large mass of active bees quickly raises the temperature in the nest until it is hot enough to kill the hornet, about 47º C (117º F). This is not quite hot enough to kill the bees, although the hornet will still manage to nip off a good number of heads before it dies, ensuring a high death rate.
While these hornets are pretty cool, don't believe everything you hear about them. It is sometimes said that a sting will kill a person, that three stings will kill a person, that the hornets can shoot their venom into your eyes, that their poison can melt human flesh... Well, there is actually a chemical in the sting that can 'eat' living tissue, but not in the scary "I'm mel-l-l-l-lting!" way you might fear. It's just mastoparan, a venom present in most bee and wasp stings. All these other myths are indeed just myths; a healthy person with no allergy to stings can handle three stings with nothing worse than blinding pain, and they do not actually spit poison into your eyes.
But they do, apparently, taste good. It has long been a tradition in Japan to eat the larvae of the Asian giant hornet, either deep fried or raw. Some energy drinks have even started including synthetic larvae secretions; the larvae secrete a juice containing specific amino acids; this juice is eaten by the adult hornets (who cannot digest solid foods), and athletes impressed with the hornets endurance and speed are quite willing to drink it too. It is said to increase the rate that the body turns fat into energy, giving athletes greater energy reserves. Whether this is true or not, there are a number of athletes that swear by it.
References:
The Social Biology of Wasps, By Kenneth G. Ross and Robert W. Matthews, 1991
http://www.vespa-crabro.de/vespa-mandarinia.htm
http://en.wikipedia.org/wiki/Asian_giant_hornet
http://www.cracked.com/article_15816_5-most-horrifying-bugs-in-world.html