The constant buzzing of cicadas is the typical sound of summer days. That buzzing also signals the appearance of our biggest wasps - the cicada killers (Sphecius speciosus). How big are they? About the size of a cicada - big enough to pick up and carry a cicada with no problem!
The only critter you might mistake for a cicada killer is the European hornet, which is nearly as big. However, the European hornet is yellow-and-black with a distinct brown band in the middle and all yellow at the end of the abdomen. The cicada killer is yellow-and-black but all black at the end of the abdomen. European hornets live in colonies, while the cicada killer is a solitary burrowing wasp.
Most important, the cicada killer is harmless to us and beneficial because it kills cicadas. Although the females are capable of stinging, researchers have found that they won't unless actually caught and placed against one's skin. Even then, the sting is probably the weakest of our stinging insects. If you disturb her burrow, the female will give a threatening buzz, but she will not come out after you.
Adult cicada killers feed on nectar and pollen. Only their larvae eat cicadas. Male cicada killers are smaller than females because they do not need to develop eggs or carry cicadas.
Cicada killers develop as larvae in burrows in the ground, emerging from the pupal stage in July and August. Males appear first, leaving holes in the ground (where they often return to spend nights). They spend a week or two setting up territories and fighting to maintain them. This is when cicada killers are most aggressive, because the males fly at any creatures that invade their territories. However, like male carpenter bees, they are stingless and can only bluff, head-butt and grapple with each other. When the females appear, a male mates with any female emerging within his territory.
Females only mate once, but males mate with as many females as possible. The female stores the sperm from her one mating in a storage organ. This allows her to select the sex of her offspring. She can release sperm to fertilize her eggs as she lays them - or not. Unfertilized eggs will become males and fertilized eggs females.
After mating, the female gets to work digging a burrow - she will not use the burrow where she grew up. Her burrow angles down gently and can be three feet long and two or more feet deep. It ends in several "rooms" that will each hold one egg.
The female hunts cicadas in trees. She stings one to paralyze it, then grips it with her legs, carrying it against her abdomen. She usually isn't strong enough to fly upward with a cicada, so she glides downward to her burrow. If it is too far away, she will drag the cicada up another tree, fence, etc., and glide down again. She may have to end the trip by dragging the cicada overland. Once, while standing in my garden, I had a cicada killer actually crawl up my leg with her prey to get altitude!
The female puts one cicada in a room and lays an unfertilized egg for a male offspring. She lays a fertilized egg for a female and supplies two or three cicadas, since it will grow larger. She seals each room with soil. The larvae will eat the paralyzed cicadas. If the prey were dead, they would rot before the larvae could consume them. When the rooms are full, the female closes the burrow and goes on to make one or more additional burrows. Adult cicada killers die by fall and the larvae remain in the burrows until the next summer.
Cicada killers only hunt the annual cicadas (dog days cicadas), not the 17-year cicadas, for the obvious reason that 17-year cicadas emerge in May. The wasps are perfectly synchronized with the appearance of the annual cicadas in summer. If the wasps emerged in May, they would have prey only every 17 years!
Although cicada killers are solitary, many often nest close to each other if the soil conditions are good for digging. So, if you have them around your home, they will probably always be there.
Send your insect questions to Claire Stuart by email at email@example.com or write her (with self-addressed stamped envelope) in care of Living Section, The Journal, 207 W. King St., Martinsburg, WV 25401.