INTRODUCTION. Yellowjackets receive their common name from their typical black and yellow color pattern. RECOGNITION. Adult workers about 3/8-5/8" (10-16 mm) long depending on the species, with their respective queens about 25% longer. Abdomen usually banded with yellow and black. Wings folded longitudinally at rest. The worker abdominal color pattern is usually distinctive for each species but because it does vary, a series of specimens may be required for identification. BIOLOGY. Yellowjackets are social insects and live in nests or colonies. The adults are represented by workers, queens and males. Typically, only inseminated queens live through winter and do so in sheltered places. In the spring, she uses chewed-up cellulose material to build up a paper carton nest of a few cells. One egg is laid in each cell and the queen feeds the developing larvae. After about 30 days, the first 5 to 7 workers emerge and take over all the work except egg laying. The nest will eventually consist of a number of rounded paper combs and are usually covered with a many-layered paper envelope. Nest size varies with species. Later in the season, larger reproductive cells are built in which queens will be reared; males are usually reared in old worker cells. The colony is then entering the declining phase. The newly emerged queens and males leave the nest and mate. Only the inseminated queens hibernate and survive the winter. The founding queen, the workers, and the males all die. HABITS. The queen will select a nesting site in the spring. Those nesting in the ground typically select areas bare of vegetation or else clear an area around the entrance. Those nesting in or on buildings are only a problem when the nest or nest entrance is located near human activity. Yellowjackets are slow to sting unless the nest entrance is approached and then they are quite aggressive. Each one can sting a number of times. Some people become hypersensitive to their stings and future stings can become life threatening. Queens may enter the living space during the winter seeking warmth or in the spring when they are looking for a nest site or just trying to get back outside. CONTROL. Yellowjackets are considered beneficial insects because their food consists mostly of various arthropods, often pest species. However, if their nest is located close to occupied buildings, recreational areas, or within structures, then control is warranted. If it is a ground nest a residual dust can be applied to the entrance hole. If the nest is located in a wall void a dust can be applied at the entrance hole. If it is an aerial nest dust can be applied to the nest opening.