Iowa Insect Information Notes

Social Wasps

Social Wasps

Social wasps such as the hornets, yellowjackets and paper wasps live in colonies in a fashion similar to the honey bees and ants. Most of the wasps in a colony are workers; i.e., the nest queen's nonreproductive daughters that build the nest, gather food and care for the queen's offspring.

Hornets build the familiar large nests of a paper-like material made from chewed wood mixed with saliva. Nests contain many tiers of cells covered by the outer shell with a single opening at the bottom. Hornet nests are usually located in wooded areas, attached to a tree branch, but may be attached to shrubs, utility poles or house siding. Each nest has only a few hundred workers that are about an inch long and dark with white, light yellow or cream colored markings on the abdomen, thorax, and face. Hornets can be aroused to sting in great numbers, but only when the nest is disturbed or threatened.

Yellowjackets are honey bee size (about 1/2 to 3/4 inch long) and black with bright yellow markings. (Honey bees are golden or brown.) Yellowjackets build paper nests similar to hornets but either in the ground, a log or landscape timber or building wall or attic. Yellowjackets are commonly observed hovering back and forth at the small nest opening or around garbage cans and other areas where they forage for food. Nests may contain up to 5,000 workers, most of which never travel more than a few hundred yards from the nest while looking for food. Yellowjacket stings are quite painful, but the wasps are usually not aggressive except when disturbed at the nest.

Paper wasps build the familiar umbrella shaped nests found hanging by a short stalk on the undersides of building eaves. Only a single tier of cells is constructed and there is no external covering over the nest. Each colony normally contains fewer than 25 wasps, but late in the season, the number may swell to over 100. Paper wasps are slightly longer and more slender than yellowjackets, and color is variable among the many species.

A social wasp colony lasts only 1 year. Paper wasps, hornets, and yellowjackets build a new nest from scratch each year and do not reuse the previous year's nest. The only wasps to overwinter are the fertilized queens. All the workers from a colony die with the first frosts.

Wasp Control

Wasps are beneficial insects that seek caterpillars and other insects to feed to their young. If a nest is located where it is out of the way and not likely to be disturbed, it is best left alone. If, however, a nest is located in a "high traffic" area such as along walks or near doorways, control is justified to reduce the threat of being stung.

Nests outdoors in walls or in the ground can be destroyed by placing an insecticide dust containing carbaryl in and around the nest entrance during the night. The dust particles will adhere to the insects as they leave and reenter the nest and control will usually be achieved within a few days. Do not plug a nest opening in a house wall until you are sure all activity within the nest has stopped.

Above ground nests on trees and houses can be treated with aerosol sprays specifically made for this purpose labeled for use against wasps outdoors. These spray cans shoot the insecticide several feet. Treat nests at night when all of the workers are at the nest and the chances of being stung are lower. Retreat in 2 or 3 days if necessary. For more information on insecticides please see " Insecticides in the Home Landscape and Garden."

Updated 07/14/2005 - 3:45pm