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(515) 294-9915
7/31/00
Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101,
drlewis@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning August 4
The Largest Wasp in Iowa
By Donald R. Lewis
Extension Entomologist
Iowa State University
Large insects always attract attention, but a wasp that is almost two inches long attracts a lot of attention. Meet the cicada killer, the largest wasp in Iowa. I describe this entomological behemoth as "fascinating," "intriguing" and "harmless." Most people describe the cicada killer wasp as "frightening," "alarming" and "unwanted."
Cicada killers appear in mid- to late summer (July and August) to dig holes in lawns, flowerbeds, gardens and along sidewalks and driveways. The holes lead to subterranean burrows where cicada prey are interred as a food supply for the wasp's offspring. The cicada killer is black with yellow marks across the base of the abdomen and reddish-orange wings. The closely related great golden digger is slightly smaller with a reddish orange abdomen tipped with black. The great black digger wasp is 1 inch long with a black body and iridescent blue-black wings.
Vigorous Diggers
The development of the cicada killer wasp starts with a hole in the ground. The female digs with her mouth and then kicks or carries loose particles to the surface. Nests go 6 to 24 inches deep and usually are made in the full sun where the soil surface is bare or the vegetation is sparse and the soil is well drained.
In our superiority over lowly bugs, we sometimes fail to admire their skills and abilities. The wasp, having dug the tunnel and terminated it with a series of enlarged cells, memorizes its exact location. In the big, wide world of your back yard she will return without fail to a spot no bigger than a Sacajawea dollar.
About mid-morning the female begins the hunt. She flies around the lawn searching the trees for cicadas; those large noisy insects sometimes called "locusts" and known for their familiar buzz during the late afternoons of late summer.
Upon locating a cicada, the female stings her prey by injecting paralyzing venom. This does not kill the cicada (a fortunate thing since a dead cicada rapidly decays to mush). Carting the cicada zombie, a load equal to or greater than her own size, is a struggle for the wasp. She straddles the prey, grips it against the underside of her body with her legs and tries to fly. The added weight prevents proficient flight and the trip is more gliding than flying. She may clamber up trees or posts to glide successive legs of her trip. If trees and posts are not available the cicada is dragged bodily across the lawn to the burrow.
Twenty to 40 cicadas are placed in the burrow until each cell along the tunnel contains one or two cicadas and a single wasp egg. What happens next is not a pretty picture. Suffice it to say that after the wasp eggs hatch, the legless, grub-like larvae consume the paralyzed "meals" left by the female.
The larvae remain inside the burrow until transformation to the adult stage early the following summer. The new wasps dig to the surface, shake themselves off and start the cycle all over again.
Solitary life style
The cicada killers and digger wasps are solitary. They live and work alone with no help in the construction of the nest or in the raising of young. The more familiar hornets, yellowjackets and paper wasps are social wasps. They build elaborate structures where the offspring are raised communally by a large brood of workers.
Social wasps are justifiably feared for the threat of being stung. They aggressively protect their queen and readily sting to defend their colony. Solitary wasps are non-aggressive and will not sting unless handled. Only female wasps and bees can sting. The males have no stinger and are harmless.
While the female cicada killer wasps are busy perpetuating the species, the males fly back and forth to patrol and defend a territory, a small section of the landscape they have claimed as their own. They fly at any and all that enter. Their dive bombing at people's heads and shoulders is a disconcerting display of machismo, but remember males are harmless because they have no stinger.
What to do?
Control of cicada killer wasps usually is not necessary. If nests are in an out of the way location they should be left alone. However, their presence in a high traffic area such as under a deck or near a door may be a threat and removal is justified.
Locate the nest openings during the daytime but treat after dark or before dawn. Sprinkle an insecticide dust (e.g., Sevin or permethrin) into the nest entrance and cover with a shovelful of soil. Repeat the next day if necessary. Males do not enter the holes. Either ignore them or control by capturing in an insect net during the day.
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