Jeffrey Hahn, Asst. Extension Entomologist
As their name suggests they catch cicadas. Cicadas are stout, winged insects common during the summer. However, people are more likely to hear them as they produce a power line like hum that is heard during the day. Once a cicada killer captures a cicada, she uses her stinger to paralyze it. She carries the cicada back to her nest where she will lay an egg on it. Once the grub-like larvae hatches, it feeds on the cicada. After it consumes the cicada, it pupates and remains in the burrow until next year.
Despite their size, cicada killers are not dangerous. While females have stingers, they are unaggressive and ignore people. They do not have an instinct to protect their nests (like yellowjackets and honey bees) and you can walk amongst them with little worry. Of course if you handle a cicada killer or it feels threaten, it can sting to protect itself.
Males on the other hand are territorial, looking to mate with females and chasing away other males. They can act aggressively if you enter an area they are patrolling. They will fly up to you, challenging you. Fortunately, it's all bluff as they lack a stinger and are harmless. Admittedly, that can be challenging to hold your ground when a large wasp is zooming around you but they can not hurt you.
Another option is to treat the nests. Keep in mind that generally broadcast spraying the areas where they are nesting is not very effective. Instead, apply an insecticide into each individual nest entrance. Dusts are most effective, although sprays can help reduce numbers. Effective active ingredients include permethrin and carbaryl. If you have trouble finding an appropriate insecticide, contact a lawn service to treat the cicada killers for you; they have access to turf products, like those containing fipronil or deltamethrin, that home residents can not find.