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Plantwise Technical Factsheet

western yellowjacket (Vespula pensylvanica)


V. pensylvanica is a social ground-nesting wasp native to western North America. (Hymenoptera: Vespidae). Vespids can be differentiated from other wasps by the following general morphological characteristics: 1) the pronotum (first segment of the thorax) is generally horseshoe-shaped in dorsal view, triangular in lateral view, and reaching the tegulae (‘shield‘, where the wings meet the thorax); 2) the first discoidal cell of the anterior (larger) pair of wings is long, about half the length of the wing; 3) the wings fold longitudinally at rest, and 4) the eyes are notched on the interior margins.

V. pensylvanica are strikingly yellow and black vespid wasps, approximately the size (1-1.5 cm) of a honeybee (Apis mellifera) but smooth and mostly hairless. From Miller (1961), V. pensylvanica is differentiated from other Vespula species by the following structures and color patterns: 1) malar space less than half as long as the penultimate antennal segment; 2) occipital carina complete; 3) apex of seventh tergite depressed, in profile the base very gradually sloping distally; 4) shaft of aedeagus without sharp teeth at base of terminal spoon; 5) eyes are completely ringed with uninterrupted yellow border (See pictures).

V. pensylvanica make large nests of hexagonal paper cells, usually subterranean, ranging from a few hundred to tens of thousands of cells (Duncan, 1939; Bohart and Bechtel, 1957; MacDonald et al., 1974; Ratnieks et al., 1996; Visscher and Vetter, 2003). Nests are often constructed within old rodent burrows or natural fissures. Within most of the natural temperate range, nests decline annually in the winter and must be founded anew each spring by a solo, overwintered, mated queen (Akre et al., 1980). In the invaded range in the Hawaiian Islands, colonies can survive and continue to grow for multiple seasons into enormous polygynous nests with high traffic rates (Gambino, 1991). Gambino and Loope (1992) estimated one multi-year, polygynous nest on Haleakala (Maui) as containing more than half a million cells.

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