Large, but mild-mannered, female cicada killer wasps (Figure 1) are buzzing across Kentucky intent on:
- Digging underground burrows and
- Provisioning themselves with paralyzed cicadas that will be food for their grub-like larvae.
The wasps will focus on these tasks over the next few weeks, generally oblivious to the stress and anxiety that they may be causing.
Why are cicada killer wasps so abundant in some areas?
Cicada killers choose sites with specific characteristics: well-drained, light-textured soils in full sunlight that are near trees harboring cicadas. They may dig along sidewalk or patio edges, as well as in flowerbeds, gardens, lawns, and fields. They are there because of the favorable conditions. Large aggregations can build up over time. An estimated 40% of the developing larvae (a dozen or more per tunnel) may emerge as adults the following year, so numbers can increase rapidly.
Are cicada killers dangerous?
Females have a significant stinger (Figure 2) that they plunge into cicadas and a venom that paralyzes them. Without a doubt, a sting would be painful. However, they are not aggressive and do not have a strong nest-guarding instinct. You can walk through areas where they are active without attracting their attention.
The buzzing noise that they make and the warning colors on the wings and body are defensive, intimidating, and discouraging to predators that see them as a large meal. When attacked, females will use their stinger to protect themselves.
As with many species, males are somewhat different. They lack stingers but are territorial. They will approach anything that enters “their area,” including people walking, mowing, using weed-eaters, or riding tractors. They may hover and challenge trespassers but are harmless. That can be easy to forget when staring down a big wasp.
Will cicada killers harm pets?
Some dogs and cats may catch cicada killers but usually just once. Those that pick females probably will be stung, remember it, and associate the experience with the buzz and warning colors. Some may have a severe reaction to the venom, especially if stung in the mouth. If that is suspected, the animal should be taken to a veterinarian immediately. Wasp flight begins in early morning and can continue until dusk. Wasps remain in their burrows at night, so encounters can be avoided by managing the activity of the pet.
Can cicada killers cause damage?
Cicada killers may dig in loose soil in gardens. A burrow at the base of a plant may disrupt the plant’s root system. If only a few plants are affected, drenching the area around the base of affected plants with water is probably the best approach. The wasps do not like wet soil; watering the plants thoroughly will settle soil back around the roots giving them a chance to survive and perhaps force the wasp to abandon the site. Do not drench soil around plants with an insecticide mix; it may damage the roots and/or result in a residue in the plant.
Cicada killers may begin to dig in sandy areas such as playgrounds or golf course sand traps (Figure 3). As much as 100 cubic inches of soil may be brought to the surface as tunnels are formed. This can be unsightly in highly managed turf and the accumulations may smother grass.
If practical, keep these areas wet or regularly churn the sand as wasps are establishing their tunnels. Sometimes skunks may dig up nesting areas to feed on cicadas and wasp larvae.
What are the tunnels like?
Cicada killer tunnels usually have a distinctive U-shaped collar of loose soil around the opening. Individual tunnels 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. The first chamber is about a foot or so from the entrance. Wasps complete their development and emerge the next summer.
Can cicada killer wasps be controlled?
Control may be desirable in situations where physical damage is occurring or the presence of the insects is causing significant distress. The wasps were controlled in a West Virginia study with sprays of pyrerthroid insecticides (cyfluthrin or cyhalothrin). Applications were made directly into the burrows or only to the entrances where 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.
Will cicada killers ever go away?
These wasps will stay at sites that meet their needs and thrive. Even if aggressive control measures kill the inhabitants, the sites will remain attractive to new settlers in ensuing years.
By Lee Townsend, Extension Entomologist