V. pensylvanica is a predatory species that feeds on a wide range of invertebrate taxa (and occasionally even on slugs) and this has great potential for negative impact on the native fauna in insular habitats. In its genus, it is one of the few species that also has a scavenging habit as opposed to a strictly predatory habit and is thus considered a major pest to humankind. Along with two other species — the "common wasp" or "yellowjacket" (Vespula vulgaris) and the "German wasp" or "European wasp" (Vespula germanica) — V. pensylvanica is part of the "Vespula vulgaris species group" which together are the most abundant and bothersome of eusocial wasps species. With a predilection for scavenging carrion that attracts it to the human food and garbage, V. pensylvanica is the most significant pest yellowjacket in western North America.
Vespula pensylvanica shares its basic yellow and black pattern with other species of wasp in genus Vespula and its sister genus Dolichovespula which are collectively known in North America by the common name "yellowjacket." V. pensylvanica, however, is the only member of its species group that has a complete yellow eye ring around each compound eye. This eye ring is also visible in queen wasps of this species.
Occasionally, the eye loop is entirely absent in males; it can be broadly interrupted in both sexes but rarely so in females. Males without a yellow eye loop can be distinguished from V. germanica by more subtle morphological differences, viz, "the deeply emarginate or spotted subantennal mark on the frons, the slender preapical portion of the aedeagus, and the much more densely pubescent apical margin of tergum". The majority of females of Vespula squamosa also have a narrow eye loop but this species shows a radically different metasomal pattern. the majority of western yellow jackets are blind, except for the queens
The length of this species's fore wing is 8.5–10.5 mm in workers, 12.5–14.5 mm in queens, and 12.5–14.0 mm in males.
Even though the specific name given it by Henri Louis Frederic de Saussure is "pensylvanica", this species is actually native across the western half of North America, in temperate zone climates. More precisely, individuals have been identified in Canada from Manitoba to British Columbia. The easternmost record for V. pensylvanica is a single record from Ontario but it is apparently not established in that province as a species. In the United States the eastern edge of its range is in Wisconsin, Nebraska, Colorado, and Texas. In Mexico it is known from Baja California Norte, México, and Michoacán.
In the Hawaiian Islands and other areas V. pensylvanica has been recorded as an introduced species. Attempts to eradicate this species from Hawaii using the toxicant bendiocarb began almost as soon as a population was discovered there in 1977. A 1988 paper revealed that V. pensylvanica was successfully attracted to canned Figaro brand tuna cat food laced with micro-encapsulated diazinon as well as, to a lesser extent, the same cat food laced with amidino-hydrazone. The color of the dispensers from which the bait was offered proved critical; translucent white dispensers were most effective.
Media related to Vespula pensylvanica at Wikimedia Commons