This is the smallest species of Vespa in Hong Kong, and certainly one of the smallest in the world (perhaps the smallest). It is easily recognizable due to its bright yellow colour; it has a black triangular patch on the central part of the thorax, and the abdomen sometimes displays black stripes due to expansion when the wasp is eating. Queens are far larger than workers and reach 25mm or more; males average 19 to 23mm, and the largest workers reach 22mm. Most workers I find are in the range of 17 to 19mm, and some only 15mm or even smaller.
Vespa bicolor is the most common species of its group in Hong Kong, and is one of the most common social wasps, along with species of Parapolybia. It can be found in a wide range of environments, and frequently appears near human dwellings.
Vespa bicolor is not at all picky regarding its choice of prey. Workers of this species target small flying insects, and tend to hunt by site. They are also fond of human food, particularly meaty items, and frequently appear at barbecue sites. This is the only local hornet which seems to like collecting cooked meat. It can thus be a pest at barbecues and outdoor events. Recently I actually saw some fly into a restaurant looking for food! And a couple of months ago, I watched with some amusement as a man had to abandon his lunch box when five or so individuals circled his food when he settled down on a park bench for an outdoor lunch. They apparently do not hurt people in their quest for food, and a small number can easily be chased away, but on occasions, when they appear in large numbers, it can be disastrous. They especially like the smell of barbequed meats and fish, as well as anything sweet. They also forage among garbage. Although it is in the genus Vespa (hornets), after reading about Vespula species (yellowjackets) in the West, I personally feel that this is the Asian equivalent. Although Vespa affinis and Vespa velutina also occasionally forage for carrion, no hornet in Hong Kong other than Vespa bicolor seems to like cooked meat. The worker in the photo below has just landed on an accidentally dropped chicken drumstick.
The nest of Vespa bicolor can be located in a wide variety of locations; under roofs, high in trees, under rocky ledges, in tree hollows and also frequently underground; more than 50% of nests I have found so far have been built either in concealed locations or inside buildings. It is generally 25 to 35 cm in diameter, and almost always spherical; it may become slightly oval if the colony did exceptionally well. It can be distinguished by its shape and light, fine appearance, with numerous arc-shaped overlapping layers on the outer envelope. Nests in enclosed spaces may take on unusual shapes according to the confines of the cavity. This species has an extremely long life cycle; the queens awake from hibernation as early as late February, and nests may be built as early as mid-March, though April to May is more usual; the colony usually dies only in late February or early March. Therefore, the period in between the death of old colonies and start of new ones is exceedingly short.
Above: A large nest about 30 feet high on a tree; the colony is starting to die in late February.
Below: A young nest built inside a temple.
Above: The same nest with the envelope stripped off to reveal the combs and workers inside.
Below: Queen and worker; the size difference is clearly visible.
Above: Nest (hidden from view) inside a tree hollow.
Vespa bicolor is in fact quite gentle; it is seldom hostile towards movement near the nest, and it is even possible to safely approach the nest to within a foot or two if care is taken to avoid sudden movement. However, when provoked, the workers will ferociously rise to the defense of the colony, although the defended radius appears relatively small. Despite its small size, it has quite a painful sting, and the vast numbers in a colony could result in severe consequences. This, coupled with the fact that it often nests near urban areas, makes it one of the more dangerous species, but still, conflict is easily avoidable. A nest will not go unnoticed for long due to the constant stream of workers returning and leaving (this species has the highest activity level near the nest of any Vespa), and therefore it is easy to avoid accidentally disturbing a nest. The queens also frequently hibernate in apartments, and sometimes fly in circles upon awaking, causing fear or annoyance. They should simply be left alone; with lights switched off and windows open, they quickly find their way out. Single queens will never attack.