Akre, R.D., A. Greene, J.F. MacDonald, P.J. Landholt, and H.G. Davis. (1981). Yellowjackets
of North America, North of Mexico. U.S. Department of Agriculture, Washington, D.C. Handbook
Vespula pensylvanica (western yellowjacket) occurs in the Canadian and Transition Zones in western North America. This species also occurs in Hawaii on the islands of Kauai (Williams, 1927), Oahu (Williams, 1937), Maui, and Hawaii (J. W. Beardsley, Univ. Hawaii at Manoa, personal commun.), and in Mexico (Ebeling, 1975; Snelling, 1970). Distribution is given in figure 62.
Nests of V. pensylvanica are usually subterranean (Bohart and Bechtel, 1957; Duncan, 1939; Smith, 1956), and most are constructed in rodent burrows (MacDonald et al., 1974). A few nests are built in other dark cavities such as in attics or between the walls of houses (Buckell and Spencer, 1950; Ebeling, 1975; Spencer, 1960). In Pullman, Wash., subterranean nests were typically 10 to 15 cm below the soil surface (fig. 63 d, e) with entrance tunnels of 10 to 30 cm (MacDonald et al., 1974).
Duncan (1939) tabulated one colony of V. pensylvanica comprised of 4,768 workers and the foundress queen. The colony probably would have grown for another month if it had not been collected, but it had already constructed a nest of 10,468 cells. He mentioned another nest of 17.25 by 16 by 10 inches but gave no other data. Table 11 lists the size of mature (producing queens) colonies collected 1971-77 in Pullman,
La Grande, Oreg. The largest nest contained 12,316 cells, and the maximum number of workers in a colony was 3,933. MocJ °1es had nests of 4,000 to 10,000 cells.
iald et al. (1975b) discussed nest associates occurring with V. pensylvanica and V. atropilosa. As a rule, at least until colony decline, V. pensylvanica has cleaner nests and fewer associates than V. atropilosa. In addition, the ichneumonid parasite, Sphecophaga yesparum burra, was found in a V. pensylvanica nest for the first time in southeastern Washington in 1977. The nest contained one adult parasite, one empty cocoon, and four intact cocoons; thus, only one of the 186 analyzed nests from 197 1-77 contained this parasite. This may be due to the behavior of V. pensylvanica workers, which immediately attack and kill introduced Sphecophaga, whereas V. atropilosa workers frequently ignore adult Sphecophaga when they are introduced.
V. pensylvanica workers will accept a wide variety of prey (Akre et al., 1976; MacDonald et al., 1974). Included are slugs, phalangids, spiders, grasshoppers, flies, cercopids, and bugs. The preponderance of prey collected were members of Hemiptera-Homoptera. Members of this species also scavenge extensively for protein, especially later in the year.
The behavior of V. pensylvanica colony members in the nest was observed by Akre et al. (1976). The division of labor among workers is not as sharply defined as in honey bees, and workers performed a number of activities during the same day. Social interactions similar to the dominance hierarchy described by Montagner (1966) for V. germanica and V. vulgaris were exhibited by the workers of V. pensylvanica. In another study (Akre et al., 1975), 80 percent of the workers foraged within 1,100 ft of the nest.
V. pensylvanica is the primary pest yellow- jacket in the West from Washington to California. Periodic population outbreaks, associated with warm, dry springs, occur every 3 to 5 years or slightly longer, which create severe problems for people engaged in logging, raising fruit, or in recreation-associated activities. A number of colonies establish their nest in yards or recreation areas, and the chance of colony disturbance resulting in stings is great. Since this species is a scavenger, it is a constant companion at picnics or at food dispensing facilities and frequently must be controlled.
Reprinted with permission from: Miller, C.D.F. 1961 Taxonomy and Distribution of Nearctic Vespula. The Canadian Entomologist Supplement 22.
Color.- Black with yellow markings.
Structure.—Malar space less than half as long as the penultimate antennal segment, (Fig. 1); occipital carina complete (Fig. 3); apex of seventh tergite of depressed, in profile the base very gradually sloping distally (Fig. 6); shaft of aedeagus without sharp teeth at base of terminal spoon (Fig. 13). Abdominal Color Patterns.—as in Figs. 25, 28, 31.
Facial Color Pattern—as in Fig. 71.
Like its close relatives V. vulgaris and V. maculifrons, this species is relatively stable over most of its range. Xanthic specimens are evidently rare; most of them come from the southern part of the range. The species is readily distinguished over its entire range.
Two female specimens recorded from east of the 100th meridian (from Dane Co.; Wisconsin and Anoka Co.; Minnesota) may have been transported to these localities by man. As yet there is no proof that the species is established in that region. The only other explanation would be a mislabelling of specimens.
Ecological Notes.—Duncan (1939) gives an excellent report on the habits of
this species. He describes its nest as terrestrial.