Coming across a giant wasp in your general vicinity can certainly put a damper on outdoor activities. In late summer you may be seeing the frighteningly large wasps known as cicada killers patrolling your lawn. Although scary looking, these ground burrowing insects are all but harmless to humans.
Cicada killers are large wasps, 1 ½ to 2 inches long, with typical
yellow wasp markings on a black body. Their wings are reddish-brown. Females are larger than males. Their nests or burrows are holes in the ground,
usually less than an inch wide, with an apron of loose soil on one side that
the female has removed.
The female cicada killer wasp catches adult cicadas—sometimes in mid-air—and paralyzes them with a sting. She then brings them to a burrow she’s dug, drags the paralyzed cicada into it, and lays an egg. When the egg hatches in a few days, dinner is waiting.
These solitary wasps do not have the nest defending instincts of other wasps and are unlikely to sting unless handled roughly. The female’s sting has been reported to be less painful than the sting of other wasps, though you probably don't want to test that. Though the cicada killer’s venom will paralyze a cicada, it is not dangerous to people. The males aggressively patrol their chosen territory but they have no stingers at all and are harmless.
Cicada killers probably pose the most threat to pets, since they don’t understand not to harass them. If they manage to catch a female they probably won’t try it again. If your pet does get stung (especially in the mouth), watch for swelling and bring them to the vet if they seem to be having a reaction.
Because they are attracted to loose, dry soil to form their burrows, they can cause some minor damage to the landscape if large numbers of females choose to nest in the same area of ground. They do not damage the roots of plants directly, but the soil they excavate from the burrows may make smaller plants unstable and can be unsightly.
They may return year after year to the same desirable spots. A large number of cicada killers may be attracted to a particularly favorable location. The best way to deter cicada killers from burrowing in a specific area is to keep the soil there moist during the late summer when they are active.
Cicada killers can be killed with wasp sprays, but it is not necessary to do so as they rarely cause problems except in large numbers. An unconventional method of eliminating them is to knock them to the ground with something like a tennis racquet and stepping on them.