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Vespula pensylvania, the western yellowjacket, is a social, ground-nesting wasp native to western North America. They aggressively protect their nests, and, like other vespid wasps, can sting repeatedly. Adult workers forage continually for high protein foods, mostly small insects, caterpillars, and spiders, and they sometimes scavenge on dead animals to feed their brood. Vespula pensylvania is found in all states west of the Rocky Mountains, from Mexico up through western Canada. Although it has a more limited distribution than either the closely-related and biologically similar common yellowjacket Vespula vulgaris or the German yellowjacket Vespula germanica (which have both recently become major pests in non-native habitats around the world, especially in the southern hemisphere) V. pensylvania also has a high potential for invasiveness. Since 1919 there have been sporadic reports of the western yellowjacket in Hawaii, and in 1978, populations there exploded to become a public nuisance and threat to endemic Hawaiian insect fauna. A western yellowjacket queen starts to build a nest in the spring, which matures into a large colony of up to several thousand workers by fall. At this time the colony declines and only new queens overwinter. However, in warm climates, such as California and Hawaii, colonies can survive longer than the several summer months they last in their native range, growing to enormous size with the potential to devastate surrounding insect populations and create a large, difficult to control public nuisance. If their nests can be located, physically or chemically destroying them are effective means of population control. Toxic baits, in which attractants are laced with insecticides and offered to workers to feed to larvae and the queen can also be successful in destroying a colony. Baited traps are also used to monitor and assess population numbers. Although Vespula pensylvania has similar yellow and black coloration patterns to other yellowjackets (wasps of the genera Vespula and Dolchivespula), the complete yellow ring around their eye is a reliable distinguishing characteristic. (CABI 2011; Kweskin 2009; Wikipedia 2011)


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