Posted: July 28, 2011
They appear each summer about the same time as their sole larval food source, dog-day or annual cicadas. Despite their large size and seemingly aggressive behavior, they are not dangerous to humans, except possibly to individuals very sensitive to bee or wasp stings.
These large wasps are about 1 ½ inches in length, but their 3 ½ to 4 inch wingspan can make them appear twice their actual size. A black abdomen with yellow stripes, orange-red head, eyes, thorax, wings, and legs, large size, and occasional “in-your-face” behavior, combine to create an intimidating presence.
Cicada killers are solitary wasps, unlike hornets and yellowjackets, which are social wasps. Each female constructs her own individual burrow in loose, sandy, dry or well-drained soil, preferably in an area with little vegetation. If you find many wasps in one area, it is because they have all found the conditions to their liking, not because they are forming a hive. The female excavates a tunnel about 1 ½ inches in diameter that may extend 12 to 24 inches in length and up to 12 inches deep, shoveling out the dirt between her legs as a dog would and creating a large horseshoe-shaped mound in the process.
Because they are solitary and not defending a nest with a queen and larvae, they are unlikely to sting and generally will ignore humans. The wasps are focused on finding a mate and then on finding prey to provision their larvae-to-be. If you happen to get in his way, the male wasp may “dive bomb” right in front of your face in defense of his territory, but he is unable to sting.
Meanwhile, the female wasp skims over the lawn in search of cicadas. If you happen to be in her way, she may zig-zag in front of you, memorizing your position as a landmark to find her way back to the burrow after the hunt. Once she has captured a cicada, she paralyzes it with her stinger, then glides or drags it back to the nest. She will lay an egg on the paralyzed cicada and then enclose it in the larval chamber, and head out again for more. When the egg hatches, the larva burrows inside the paralyzed cicada to feed on it, then overwinters as a mature larva until pupation the following summer.
There is only one generation per year, and the adult wasps live for only about two months, from July to September, feeding on plant sap and nectar. As much as possible, ignore them during this time if you can. However, if they become a nuisance by nesting in an area with a lot of human activity, such as a deck, patio, or pool area, you may need to take steps to control them.
If there are only a few, you can take aim with a tennis racket to knock them down and smash them. For a few nests in a small area, a piece of clear plastic tarp laid over the ground and secured may discourage the wasps from staying.
If the wasps are more numerous, you may need to resort to insecticides. Dust formulations of a labeled insecticide such as carbaryl or a synthetic pyrethroid are the most effective. Sprinkle the dust into the burrow opening, either in late evening or early morning, when the wasps are relatively inactive. Apply it early enough in the season to catch the female while she is still provisioning the nest. The wasp picks up the insecticide on her feet as she moves in and out of the burrow; you should not disturb or fill in the opening. For any pesticide, read and follow the directions for application carefully.