Wasps, Our Friends in the Garden
Lynn Watts
Bellevue, Washington
Reprinted from the Seattle Chapter newsletter

Unfortunately, the widespread belief that wasps are pest and should be exterminated persists even among otherwise knowledgeable gardeners. Contrary to this mistaken notion wasps are very beneficial insects.

Wasps are carnivorous insects and, as such, consume a tremendous quantity of soft bodied insects such as aphids, caterpillars, etc. Although the adult wasps are generally nectars eaters, they prey on many varieties of insects; they actually pre-chew these insects and bring them to the nests to feed to their young larvae.

In the spring a young, mated female chews wood to build a small, globular nest of wood pulp and saliva. The first generation to hatch consists only of female workers. They bring food continually to the larvae which have hatched from eggs laid by the over-wintered queen. The nest consists of many layers of cells covered on the outside with a wood pulp sheath with an opening at the bottom. Later in the summer male wasps emerge from unfertilized eggs and mate. During the late fall and early winter all the wasps die except for young, mated females who over winter in the ground or under debris to emerge in the spring and carry on the cycle.

As most people know, bees can only sting once as their "stinger" is barbed and cannot be withdrawn without fatally injuring the bee. Unlike bees, however, wasps can sting repeatedly because their stinger is not ripped out of their body when used.

The three most common varieties found in our gardens here in Western Washington all belong to the genus Vespula and are commonly called yellow jackets, hornets and bald-faced wasps.

The Western yellow jacket, Vespula pennsylvanica , build their nests in the ground or in rotting logs or stumps. Female yellow jackets can sting repeatedly and will do so if their nest is threatened or disturbed.

The sandhills hornet, Vespula arenaria , generally called yellow jacket by most people, is probably the most abundant wasp found in the Puget Sound region. The female builds paper-like, hanging nests of wood pulp and saliva. These nests, sometimes as large as a football, can be seen hanging under the eaves of houses or built in shrubbery, sometimes high up in the trees but generally closer to the ground.

The third most common species of wasp in the Pacific Northwest is the bald-faced hornet or bald-faced wasp, Vespula maculata . Generally a little larger than the other species, this wasp is distinguished by black and white or yellowish-white markings on the face and thorax. Like the other two species of wasps common in the Pacific Northwest, the bald-faced wasp is responsible for the destruction of large quantities of aphids, caterpillars and other soft bodied insect pests.

In our garden we try to leave one or two wasps nests intact during the summer to assist in insect control and we urge you to do the same. It is far better for all of us if we use natural predators than pesticides to control unwanted inspect pests.

Lynn Watts, a member of the Seattle Chapter, is the ARS Western Vice-president.