For Release July 16, 2002

Large Wasps Not As Threatening As They Look

by Chuck Otte, Geary County Extension Agent

Shortly after the cicadas (locusts or harvest locusts) start calling every summer, I start to receive phone calls about giant wasps. These wasps are huge, over an inch in length. They are very heavy bodied with reddish brown wings and a black abdomen with bright yellow markings. These wasps dig burrows in the ground often in flower beds or next to sidewalks and driveways. The entrance to these tunnels is often surrounded by a nice pile of finely ground dirt. If there are several of these large wasps around they may chase each other and fly rapidly around humans or pets in the area.

As frightening looking and as threateningly as they act, these rascals are not nearly as menacing as they first seem. These wasps are commonly known as Cicada Killers. They are in a group of wasps known as digger wasps. Digger wasps are usually solitary nesters meaing that there is one adult queen/female per tunnel. The male cicada killer has one function in life. Be available to mate with the females. They feed on pollen and like most male bees and wasps, are quite useless, and stingless. The female finds cicadas, stings them to paralyze them then drags them up a tree to get enough altitude to establish flight and then takes the cicada back to the tunnel.

Once at the tunnel, the cicada killer drags the paralyzed cicada down into a prepared chamber where it is buried with a newly laid egg. It is important to note that the cicada is not dead, only paralyzed. If it was killed, it would decay before the cicada killer larva could eat it. (What a great script for a bad science fiction movie!) When the wasp egg hatches, the young larva has plenty of food to see it through to adulthood.

There is a big difference between solitary wasps, like the cicada killer, and social bees and wasps like honeybees, bumblebees, paper wasps (polistes wasps) and yellowjackets. Social bees use their stinger in a defensive manner. They only use it to protect themselves and the colony. The active compounds in the venom are meant to create a great deal of pain, especially in mammals.

Solitary wasps use their sting as an offensive weapon. They use it to paralyze food to take back to the nest. These wasps will only sting a threatening species as a last resort. Their sting, while creating a certain amount of pain in humans, is not designed to optimize discomfort, but to paralyze prey. Their venom is equipped with quite different compounds. So while the cicada killers look mean and nasty, they will seldom sting unless you really aggravate them.

Reducing cicada killers around your home and yard can be a challenge. Filling in the holes will not work as they will just dig them back out or dig new holes. Spraying individual wasps with the wasp spray may be as effective as any other treatment. If you have many nest holes you may want to use the insecticide Sevin in the dust formulation. Sevin is very toxic to bees and wasps. If you liberally place the Sevin powder into the next entrance, the female will come in contact with it as she goes about her business and will die in a few days.

Cicada killers are essentially harmless. They feed on cicadas only and will only be around through early September at the latest. Tolerance is the best policy, especially if they are nesting away from active play and use areas of your yard. If control is warranted, late evening will probably be the best time to apply these treatments.


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