Social Wasps Vespidae

In contrast to the relatively innocuous solitary wasps, social vespids are very defensive and will sting readily. This usually occurs in proximity of their nests but also occurs at foraging sites. Vespid wasps are unique in that they usually fold their wings longitudinally at rest. The yellowjackets and hornets (vespines) and the paper wasps (Polistesspp.) are responsible for most stinging cases in North America. Vespine nests consist of horizontal, rounded combs

FIGURE 19.16 Aerial paper nest of baldfaced hornet, Dolichovcspula maculata (Vespidae), in tree. (Photo by R, D. Akre.)

attached one betow the other, usually covered with a mul-tiiayered paper envelope (Akre et al., 1981; Ross and Matthews, 1991). Some yellowjacket species build nests in exposed aerial locations (Fig. 19.16), whereas others build them in subterranean sites (Fig. 19.17). A few construct their nests in both situations. Colony size ranges from fewer than a hundred to several thousand individuals. Colonies are typically annual and are initiated by a single inseminated queen; she is the only member of the colony to overwinter. During early spring (April-June), the queen begins to construct a nest, lays eggs, and then forages for arthropods to feed the developing larvae. After the first group of workers emerge, they assume most colony functions of foraging for food, fiber, and water

FIGURE 19.17 Exposed underground nest of eastern yellowjacket, Vespula maculifrons(Vespidae), (Photo by H. Reed.)

and taking care of the larvae. The queen no longer leaves the nest after this time but assumes her primary function of laying eggs. Some species scavenge for dead organic material as a protein source for their larvae. This behavior frequently brings these wasps in contact with humans near garbage or other refuse and at picnic and recreational sites.

Perennial colonies sometimes occur when the new queens that emerge in the fall mate and then rejoin a colony. This is most likely to occur when the foundress queen has died or is losing her influence over the colony. These polygynous colonies can become perennial and contain tens of thousands of workers. Large perennial colonies of V. vulgaris, V. pensylvanica, V. germanica, V. squamosa, and V. maculifrons have been reported in the United States, usually in subtropical areas such as Florida or in moderate climates like that along the California coast. These colonies often have multiple entrances and more than 80,000 workers. Such nests are dangerous to destroy even by experienced people.

Yellowjackets (Dolichovespula and Vespula)

"Yellowjacket" is an American term that is used for all species of wasps in the genera Dolichovesptila and Vespula. The name refers to the yellow and black patterns of most species (Fig. 19.18); however, some species are black and white, such as the baldfaced hornet, Dolichovespula maculata. There are 19 species of yellowjackets in North America (6 Dolichovespula spp. and 13 Vespula spp.). Species are distributed transcon-tinentally in the United States, but most species occur primarily in the northern areas of the country (Akre eta/., 1981). True hornets (Vespa) are larger than yellowjackets, with body lengths of 20—25 mm in the workers. There is only one true hornet that occurs t t

FIGURE 19.18 Workers of the western yellowjacket, Vespula pensylvanica (Vespidae) guarding the entrance of their underground colony. (Photo by Roger D, Akre.)

Comparison of Colony Parameters and Foraging Behavior of Yellowjackets in North America: Colony Decline is Defined as the Period When Reproductives Emerge

Yellowjacket

Distribution

Foraging behavior

Colony size

Colony decline

¿¡ermanica

Transcontinental

maculifrons

Eastern

pcnsylvanica

Western

vulgaris

Transcontinental

flavopilosa

Eastern

Vespula atropilosa

Continental

acadica

Continental

consobrina

Continental

Dotiehovespula

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