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BY SUSIE FORK

October 2003: Wasps are an incredibly diverse group of insects in terms of numbers of species and of lifestyles. Many are predators or parasites of other insects. (Some are even parasites of other parasites!) Some induce galls to form in plants while others are leaf miners during their larval period. Along with bees and ants, they are placed in the order Hymenoptera, some of whose members form complex social groups. Most of the wasps commonly seen are in the family Vespidae (yellow jackets, hornets, paper wasps, and potter wasps). These medium-sized wasps, typically 10–15 mm long, are often black and yellow or brown and yellow. California has more than 100 species of vespids, including yellow jackets and hornets (subfamily Vespinae), paper wasps (Polistinae), and potter wasps (Eumeninae). Although the social wasps are the most conspicuous members of the family, the majority actually tend solitary nests. Most vespids are predators of insects, particularly of moth and butterfly larvae (Lepidoptera), as well as many other arthropods. Predatory wasps typically offer insect prey to brood while fueling themselves with nectar, fruit, and other sugary foods. Yellow jackets and hornets form highly social colonies of one single queen and all of her offspring workers. By contrast, paper wasps nests are jointly constructed and tended by several unrelated queens. Potter and other vespids, on the other hand, are strictly solitary nesters.

A vespid wasp nest in an oak tree (more about this photo).

Yellow jackets, hornets, and paper wasps nest in many locations, both aerially (in trees, under roof eaves), and subterranean (e.g. vacant rodent burrows) and nests are constructed of wood pulp. Yellow jackets mostly nest in the ground, while hornets and paper wasps build structures above ground, though the terms yellow jacket and hornet are interchangeable. Yellow jacket and hornet nests consist of a papery envelope enclosing multiple tiers of hexagonal combs. Paper wasps build a single comb of cells without the external covering. Potter wasps make small mud “pots” attached to surfaces or build mud cells in hollow plant stems. Once her eggs are provisioned with caterpillar prey, potter wasps offer no other care.

Yellow jackets and hornets, in contrast, tend nests beginning with spring colony founding by a single queen. The queen constructs a small comb of cells, each containing a single egg and she alone forages and feeds her developing brood. The adults of this first generation then assume all colony duties including nest construction, rearing brood, and colony defense, while the queen remains in the nest and lays many eggs. Workers expand their nest by adding additional tiers of combs, and by late summer colonies can contain several thousands of workers. As fall approaches many workers are aloft, searching for food resources needed by the active colony. Workers also construct larger brood chambers then, and larvae in these cells that are fed extra food and “royal jelly” develop into queens rather than workers. The queen also lays unfertilized (male) eggs. Emerging males and queens depart and mate. While males, founding queens, and colonies do not survive past winter, new queens find winter retreats and begin colonies the following spring.

A vespid wasp nest in a burrow (more about this photo).

From a human standpoint, wasps are beneficial because they prey on insect pests of cultivated and ornamental plants. In addition, although they are not specialized pollinators, native wasps may add to the pollinator workforce as they search for sugar resources. However, social wasps in particular are highly defensive of their nests and can sting with little provocation. A sting to most people is merely unpleasant, but can be life threatening to those allergic to wasp venom. Although nest removal may occasionally be necessary in areas frequented by people, the wisest strategy is to keep a respectful distance from an active wasp nest rather than disturbing these beneficial insects.