Several species of large wasps in Nebraska dig burrows in the soil in the midsummer. The cicada killer wasp is alarming to some because it is huge...it can be two inches long! It is black with yellow markings on the thorax and abdomen with rusty colored wings. Barb Ogg contributed the photo of a cicada killer wasp on basil. Another species, sometimes referred to as the steel-blue cricket killer, is about 1-1/4 inches long and is a beautiful metallic blue color with black wings. Jim Kalisch, UNL Extension with the Department of Entomology, shared his photo of the steel-blue cricket killer.
Both these species are solitary wasps. This means each wasp lives independently and does not depend on other members of a colony to share in the raising of young or maintaining a nest. These solitary wasps usually paralyze insects or spiders that become food for the next generation of wasps.
Female cicada killer wasps capture, sting, and paralyze annual cicadas in July and August and place them in cells located at the end of a tunnel they have dug in the ground. Each tunnel is about ½-inch in diameter and extends 10 to 20 inches into the ground. After placing one or two paralyzed cicadas in each cell, the female deposits a single egg on the cicada and then closes the cell with dirt. Each burrow may have as many as 10 cells. After only a day or two, the larval wasp emerges from the egg and feeds on the paralyzed cicada. It passes through the winter as a fully developed larva, pupates the next spring, and emerges as the adult wasp in summer.
The steel blue cricket hunter has a similar life cycle, but provisions its cells in the ground with crickets. Iridescent females often are observed on the ground, flicking their wings while keenly watching for an unguarded cricket.
Unlike yellow jackets and other social wasps, these solitary wasps are not aggressive. The females can sting (after all they sting and paralyze their prey), but they don't attack people unless they are handled. Males cannot sting and do not dig in the soil, but hang around in groups near breeding locations, aggressively posturing for available females.
These wasps prefer soft soil or sand to dig their burrows and rarely dig in established areas. They choose sites with well-drained, light-textured soils in full sunlight near trees harboring cicadas.
Because both these wasps rarely sting people, control is not justified; however, these wasps can cause homeowner stress because of all the activity around the nesting site. If burrows are concentrated in an area, consider covering the soil with shade cloth, plastic sheets or plastic mesh to prevent the wasps from digging in the soil. Dust formulations of insecticides can be used in the burrows, but may not completely prevent emergence of wasps the next year. Some studies have shown liquid pyrethroid insecticides, applied into the burrows can be helpful. As always, read pesticide labels carefully prior to purchase and again before using. Jim Kalisch, UNL, photographed signs of cicadad killer wasp nests at a retention wall.
Being patient always works well...these wasps die after they have provisioned their burrows.