Several species of wasps patrol landscapes by air or ground. A few nest in loose, well-drained soil in gardens, flowerbeds, and along sidewalks. Usually, they have warning coloring and intimidating behaviors, but they do not attack without provocation. If left alone, they go about their duties with a single-minded purposefulness.
Cicada Killer Wasps
Cicada killer wasps are intent upon these tasks:
1) Digging underground burrows and
2) Providing paralyzed cicadas that will be food for their grub-like larvae (Figure 1).
Cicada killer wasps (CKW) will focus on these tasks for the next few weeks, generally oblivious to the stress and anxiety that they may be causing to nearby humans.
Their buzzing noise and warning colors on their body are defensive, meant to intimidate and discourage predators that see them as large meals. Females have significant stingers (Figure 2), which they plunge into cicadas to inject paralyzing venom. Without a doubt, a sting would be painful. However, CKW are not aggressive and do not have a nest-guarding instinct. People can walk through areas where CKW are active without attracting attention from these wasps.
Cicada Killer Wasp Site Selection
These solitary wasps choose sites with specific characteristics: well-drained, light-textured soils in full sunlight that are near trees harboring cicadas. In landscapes, they may dig along sidewalk or patio edges and in flower beds, gardens, lawns, or fields. They are present because of the favorable conditions. Large aggregations can build up over time. An estimated 40% of developing larvae (a dozen or more per tunnel) may emerge as adults the following year, so numbers can increase rapidly.
Cicada Killer Wasp Tunnels
Cicada killer tunnels usually have a distinctive U-shaped collar of loose soil around the opening. Individual tunnels are can range from 30 to 70 inches long and may run 12 to 15 inches below the surface. There are an average of 15 egg-shaped cells as side chambers to the tunnel, each containing 1 to 3 paralyzed cicadas and a developing wasp larva. Usually, the first chamber is about a foot or so from the entrance. Development will be completed when wasps emerge the following summer.
Golden Digger Wasps
Golden digger wasps are large, solitary, ground-nesting wasps that capture and bury katydids and crickets as food for their developing larvae. The narrow-waisted adults (Figure 3) visit flowers for pollen and nectar, so they may serve to some extent as pollinators. In some cases, the wasps may tunnel in tilled soil near the base of a flower or vegetable plant, causing the plant to wilt.
Blue-winged wasps (Figure 4) fly search patterns just above turf to detect infestations of white grubs, especially larvae of the green June beetle. In addition to shiny blue-black wings, they have a pair of yellow bars just in front of their rust-red abdominal tip. These easily recognized wasps will land to lay their eggs on white grubs in the soil. They do not excavate brood tunnels like the previous two species; their larvae develop where the grubs are found.
Velvet ant (also called cow-killer) is a wasp, not an ant. The straight antennae of this insect is a feature that distinguishes them from ants, which have elbowed antennae. Larvae of these wandering wasps develop on subterranean larvae or pupae of different species of beetles, flies, moths, etc. Venom injected through a long stinger immobilizes the host. Velvet ants can inflict a very painful sting if handled.
By Lee Townsend, Extension Entomologist