Vespula pensylvanica

The western yellowjacket (Vespula pensylvanica) is a Nearctic species of wasp in the genus Vespula. It is native to regions of North America, largely in areas with northern temperate climates. Its reproductive behavior is constrained by cold weather, which successfully reduces the number of western yellowjackets in cold months. However, in the absence of cold weather, this wasp's population can explode. The western yellowjacket has become particularly invasive in the Hawaiian Islands, resulting in their label as a major pest. V. pensylvanica was originally named by de Sausser in 1857; it falls into the subgenus Paravespula, within Vespula. Paravespula consists of 11 species, which have been divided into four groups on the basis of morphological differences. V. pensylvanica falls into the same group as V. germanica. With the exception of Allovespula, the subgenera recognized within Vespula are natural groups. The separation of Rugovespula and Parvespula appears to be monophyletic; however, this is not well established. The western yellowjacket shares the basic yellow and black pattern with other species of social wasps in the genus Vespula. As a result, it is often misidentified. Specifically, it closely resembles V. germanica. Though both species have a similar diamond-shaped black mark on the first tergum, V. pensylvanica can usually be differentiated by the continuous yellow ring (often referred to as an eye-loop) present around each eye. The eye-loop is not always present, however. Though few females lack this distinguishing characteristic, males often do not have the eye-loop. In such cases, V. pensylvanica can be identified by a spotted mark on the frons below the antenna, a slender aedagus, and a denser apical region of tergum 7. The fore wing length ranges from 8.5-10.5 mm for workers, 12.5-14.5 mm for females, and 12.5-14.0 mm for males. Western yellowjackets build large nests made of wood fibers, enclosed in a hexagonal paper envelope with a small 10– to 30-cm entrance tunnel at the bottom. Nests are usually found 10–15 cm below ground or in other dark cavities, such as rodent burrows. The western yellowjacket is native across the western half of North America, in temperate zone climates. Its range overlaps with that of V. atropilosa. Individuals have been identified in the Canadian and Transition Zones in western North America. It has been found in all states west of the Rocky Mountains, from Mexico through western Canada. It is also found in Hawaii on Kauai, Oahu, Maui, and Hawaii.V. pensylvanica can be found in open forest, prairies, urban zones, gardens, parkland, meadows, and houses. Colonies are initiated by the queen. After emerging from the diapause when winter ends, the fertilized queen searches for a nest site. When it is located, a small nest is formed. The queen continues to forage for construction materials and food until four to seven workers have emerged. At this point, the queen focuses solely on laying eggs and the nest continues to expand. Between August and September, males and queens are produced, which then leave the nest and mate. The nest begins to decline around this time. The males eventually die, and the inseminated queen begins diapause. The inseminated queen is the only member of the colony to survive winter. Longevity of the workers varied with colony activity and development, with the lifespan of the earliest-born workers averaging 22 days and the latest-born workers averaging 40 days. Typically, colonies are monogynous and annual. In these colonies, attempts of other queens to enter result in fierce fighting between the intruder and the residing queen and/or workers. Perennial colonies, though, have been reported, containing numerous queens. Most perennial colonies have larger nests and more individuals. As the size of a colony increases to the point where at least 30 workers are foraging at the same time, competition develops between workers. Often, one worker will attack the prey of another worker, resulting in neither worker bringing back prey. Older workers are more successful in attacking. They may also maul to exhibit dominance over nest mates; mauling entails one individual chewing another individual that remains motionless throughout. Generally, this occurs between two workers, with the aggressive worker beginning the mauling process when a returning forager enters or is near the entrance of the nest. At any given time, certain individuals repeatedly express mauling tendencies and recipients remain constant. Over time, the recipients become the maulers as they approach old age. As the colonies decline, mauling becomes less frequent.