This is the time of year when entomologists get calls about German shepherd-sized wasps invading people's yards. While maybe not quite as big as a dog, this year two very large wasps are common in backyards. One we see on a fairly regular basis and one not so often or numerous. These wasps are from 1 to 2 inches in length and have good sized stingers, so it is understandable that people are afraid of them. The good news is that they are fairly docile, meaning they are not aggressive in defending their nests, unlike German yellow jackets and other paper wasps. The bad news is that they are very hard to control. The two wasps are the cicada killer and the spider hawk.
What makes it difficult to control these wasps is that they are solitary, meaning they do not share a nest, and do not live in the holes they make. There may be many in a given area, but they will have individual nests, usually in the ground. Solitary wasps put paralyzed insects or spiders inside the nest as food for their offspring. The paralyzed victim does not die immediately, as that would spoil the food for the young larvae (grubs). Instead, the larvae feed on the fat bodies and muscles of the victim first, keeping the heart and nervous systems intact until the end. This is somewhat gruesome but efficient.
The first wasp in question is a regular visitor in all parts of the state. The cicada killer has the standard black and yellow markings with rusty colored wings, but is very large compared to other wasps, about 1 ½ to 2 inches in length.
Female cicada killer wasps capture annual cicadas in July and August and place them in cells located at the ends of tunnels they have dug in the ground. Each tunnel is about the size of a dime/quarter and can extend 24 inches or more into the ground. One or two paralyzed cicadas are placed in each cell, and a single egg deposited before the cell is closed by the female, who flies away, never to return. The wasp grubs feed on the cicadas and develop into wasps that emerge the following summer.
The spider hawk is a large beautiful dark, shiny blue wasp, slightly smaller than a cicada killer. A characteristic is the curled or spiraled position of the female's antennae. Spider hawks are similar in behavior but as the name suggests, prefer spiders as entrees for their young. Some species will build mud nests in buildings. Both wasps will capture other insects occasionally, depending on what is available.
The cicada killer and spider hawk, like other solitary wasps, have the capability to sting, but won't unless handled or threatened. Only female wasps have the ability to sting. Stings inflicted by solitary wasps are usually not severe but reaction varies with each individual.
Wasps are generally beneficial and a nest in an out of the way location where it is not likely to be disturbed should be left alone. If a nest is located where problems could arise, such as under a deck or near an often used door, you can try to remove them. It has been suggested to try placing an outdoor use insecticide dust containing carbaryl in and around the nest entrance during the evening. As a side note, whenever using a pesticide, read the label carefully and follow the directions. It's the law!Theoretically the dust particles will adhere to the wasps as they come and go from the nest. Cover the nest opening with a shovelful of soil after all activity has stopped. If you have many nests this will be difficult to do. Again, these are not aggressive wasps and will not normally sting unless handled.