Cicada killers (Sphecius speciosus) are on the prowl, and there have been many inquiries about them at the Master Gardener plant clinics.
Cicada killers are solitary wasps with yellow banding on their abdomens. They appear in late July and early August and resemble large, black hornets. These insects are considered beneficial because they help control the annual cicada (Tibicen spp.) population. However, the excavating and burrowing that they do in open, dry ground when constructing their nests can be a nuisance for gardeners and homeowners.
Cicada killers are usually non-aggressive, although the male may investigate a person who invades its territory to determine that it is not another male cicada killer. Males are unable to sting. The females can sting but do so only when handled or disturbed because they lack the instinct to guard their nest as the honey bee does.
The singing of the annual cicadas causes the adult wasps to come above ground out of hibernation. On their search for annual cicadas, they will stop and drink nectar and water from gardens. Once the female cicada killer has found and paralyzed a cicada, she will carry it back to her underground nest. She places her prize in a nest cell, lays her eggs on it and seals up the cell. The larvae hatch in a few days and begin to feed upon the cicada before they form a cocoon to pupate for the winter and early spring.
For gardeners concerned about the safety of children or pets, U of I Extension suggests planting ground covers and grass to prevent bare spots, adding mulch, and using irrigation to deter nesting. An application of a carbamate-based chemical product to the nest will kill cicada killer adults and their larvae, but killing this beneficial insect is discouraged.