The median wasp (Dolichovespula media) is a species of social wasp of the family Vespidae found throughout Europe and Asia. It builds aerial paper nests often in shrubs or trees, and occasionally under the eaves of buildings. It is most common to see this wasp between May and October during its 3.3 month colony cycle. Behaviours of this wasp include nest defense, curling which is believed to function in brood incubation, and gastral vibration which is involved in larval feeding. The median wasp has a sex determination system that results in a high level of relatedness within the colony. This species is not usually aggressive but will sting if they feel their nest is threatened. Most foraging in the nest is done by the workers once the first ones reach adulthood. These workers forage for insects, nectar, and wood for nest construction in temperatures as low as . The median wasp is known to be occasionally affected by the fungus Cordyceps sphecocephala and the Cricket paralysis virus.
Taxonomy and phylogeny
The median wasp was first classified by Anders Jahan Retzius in 1783. This wasp is part of the subfamily Vespinae which includes all hornets and yellowjackets. It is part of the genus Dolichovespula, a genus whose species include the tree wasp (D. sylvestris), the Saxon wasp (D. saxonica), the bald-faced hornet (D. maculata), the Arctic yellowjacket (D. norvegicoides), and the parasitic hornet (D. adulterina).
Description and identification
D. media is a medium to large species of wasp around in length with yellow and black stripes on its abdomen. It can be identified by its yellow clypeus with a thin black central line and large areas of yellow behind the eyes and on the ocular sinus. The median wasp also has a shiny black thorax with four yellow spots that are tinted orange or red. Queens are often mistaken for hornets due to their reddish colouration, but can be distinguished by their thoracic spots and deep black color.
Distribution and habitat
The median wasp has a Palearctic distribution and is found throughout Europe and temperate regions of Asia all the way east to Japan. It prefers temperate climates and high humidity. This species was identified in the United Kingdom for the first time in 1980 after having spread there from continental Europe. It has also been sighted in New Zealand, but it is not known if the wasp is widespread in the area or if this was an isolated occurrence.
D. media builds aerial paper nests above ground. These nests are typically found in shrubs, trees, and sometimes under the eaves of buildings. Nests are made of paper that comes from the digestion of wood and are generally wide and tall. Colonies are often found in both urban and rural areas. These wasps prefer to build nests close to the ground where humidity levels are higher as well as in open areas where the nest is subject to large amounts of sunlight.
Colony cycle
The colony cycle of D. media is about 3.3 months and occurs between early May and the end of August. The nests are initiated in early May when a single queen emerges from her overwintering hibernation site. All queens in the same region tend to emerge from hibernation and initiate nests at about the same time and do not disperse over weeks or months as in some other species. The queen rears about 10 workers by herself and it takes about 30 days for these workers to mature to adults from eggs. The first workers emerge around early June and start small cell building, where males and workers will be reared, and begin foraging for the colony. The colony continues to grow and large cell construction begins in early July which is where the new queens and some males will be raised. A mature median wasp nest will have about 1000 total cells. Around 320 will be small cells, 680 large cells, with an average of 800 wasps reaching adulthood. The first queens will emerge in early August and disperse to find hibernation sites. The rest of the workers, the old queen, and the males will begin to die off with the colony terminating by the end of August. However, workers are sometimes seen as late as early November.