Cicada Killer Wasps

Cicada killer wasps are active across Kentucky during July and August.  Females are intent on their tasks of: 1) digging underground burrows and 2) provisioning them with the paralyzed cicadas that will be food for their grub-like larvae. These insects are focused on their tasks and pay no attention to anything else unless handled or mashed by bare feet.

Stingless males, on the other hand, are territorial and quite ready to investigate anything or anyone who passes through “their” area. They also seem to be attracted to vibrations from weed eaters, mowers, and tractors. This can lead to a disturbing experience with intimidating, but harmless, insects. The wasps remain in their burrows at night so encounters can be avoided by managing the activity of pet and lawn or garden chores.

Figure 1. Female cicada killer carrying a cicada to her burrow (Photo: Lee Townsend, UK)

Figure 1. Female cicada killer carrying a cicada to her burrow (Photo: Lee Townsend, UK)

Cicada Killer Wasps & Pets

Will cicada killers harm pets? Some dogs and cats may catch cicada killers out of curiosity but usually only once. Those animals that pick females probably will be stung, remember it, and associate the experience with the buzzing sound and warning colors. A few may have a severe reaction, especially if stung in the mouth.  If that is suspected, take the animal to your veterinarian immediately.

Burrowing Site Selection

Burrowing sites selected by cicada killer wasps have some specific characteristics. They are in open, well-drained, sandy or light-textured soils that allow efficient digging. This is an important feature because the wasps may excavate as much as 100 cubic inches of soil when forming tunnels. Soil brought to the surface can be unsightly in highly managed turf and may smother grass, causing bare spots. The wasps often dig along sidewalk or patio edges, in flower beds, gardens, or lawns.

Site characteristics are why the wasps are present and why their numbers increase over time. An estimated 40% of the developing larvae (a 12 or more per tunnel) may emerge as adults the following year. That is an impressive population growth rate and numbers can build rapidly. Treating burrows in an attempt to control these insects may provide some temporary relief but doesn’t change the area’s attraction to the wasps; they will be back.

Cicada Killer Wasp Tunnels & Insect Development

Cicada killer wasp tunnels usually have a distinctive U-shaped collar of loose soil around the opening. Tunnels can range from 30 to 70 inches long and may run 12 to 15 inches below the surface. The first chamber is about a foot or so from the entrance. There is an average of 15 egg-shaped side chambers along the tunnel; each contains 1 to 3 paralyzed cicadas and an egg that hatches in 2 to 3 days. The grub-like wasp larva feeds for about 10 days, leaving only the cicada’s outer shell. During fall, the larva spins a silken case, shrinks, and prepares to overwinter. Development will be completed when wasps emerge next summer. There is one generation each year.

Management

Control may be desirable in situations where physical damage is occurring or the presence of the insects is causing significant distress.  Cicada killer wasps were controlled in a West Virginia study by sprays of pyrethroid insecticides (cyfluthrin or cyhalothrin).  Applications were made directly into the burrows or only to the entrances; the wasps contacted the insecticides as they entered and left.  Broadcast sprays over the area where cicada killers were nesting were not effective in reducing their numbers.

The most likely non-chemical control option involves scattering soil around the burrow entrances and keeping these areas very moist by drenching  regularly with water. The wasps do not like moisture and this may cause them to find a new location. Also, the soil collar may be an important burrow-finding cue; without it, the wasp may have trouble locating the entrance. This approach requires a persistent effort, so it is most practical for small areas.

 

By Lee Townsend, Extension Entomologist

 

 

Posted in Lawn & Turf