Iowa Insect Information Notes

Spider Wasps

Spider Wasps

Spider wasps are common insects in Iowa that usually go unnoticed until they are encountered indoors as an accidental invader. Spider wasps are medium sized insects (approximately 1/2 inch long), slender with long spiny legs. The body is usually dark and the wings are smoky black or blue. The wasps are very active and the wings are jerked continuously as the wasp runs about on the ground searching for prey. A prominent characteristic is the curled or spiraled position of the female's antennae.

Spider wasps are solitary; that is, each female works alone to provision a nest for her offspring rather than working in a social colony. Therefore, spider wasps are less likely to sting than other common wasps. They will, however, sting if handled or threatened.

As the name implies, spider wasps feed on spiders. The female wasps capture and paralyze a spider and then prepare a cell for it in a branching tunnel in the ground or in rotten wood. A few species construct mud cells that are provisioned with the paralyzed spiders. One egg is attached to each spider, which serves as food for the larva after hatching.

Spider wasps in the house are probably accidental invaders that have wandered in from outdoors by mistake. This annoyance is most common in late summer and fall as the wasps search for winter hibernation sites. Spider wasps may also be encountered indoors if rotted wood within the structure is being used for nesting.

There is no special control for spider wasps. Those found indoors can be swatted or lightly sprayed with a ready-to-use household aerosol insecticide. For more information on insecticides please see "Insecticides for Indoor Use."

Updated 07/14/2005 - 12:54pm