Tarantula Hawks, a.k.a., Pepsis Wasps, have the most painful sting of any insect, and they live here in the southwestern desert. There are 15 species in North America, some up to four inches long. The most common species in Arizona appears to be Pepsis formosa, a bluish-black wasp with orange wings. These can get up to two inches long.
Just how painful is the sting? Well, on the Schmidt Sting Pain Index, Pepsis wasps (and Bullet Ants) register a 4. Africanized bees, yellow jackets, hornets, and bumble bees register a 2. Dr. Justin Schmidt, an entomologist, recently retired from the U.S. Department of Agriculture’s Tucson Carl Hayden Bee Research Center, allowed himself to be stung by a variety of insects so he could judge the amount of pain. How’s that for a job? Schmidt poetically describes the Pepsis wasp sting as “Blinding, fierce, shockingly electric. A running hair drier has been dropped into your bubble bath.” (He describes the sting of a Bullet ant as pure, intense, brilliant pain. Like fire-walking over flaming charcoal with a 3-inch rusty nail in your heel.) The pain from a Pepsis wasp sting is said to last only three (very long) minutes.
Although their sting is traumatic, Pepsis wasps are not aggressive and it takes provocation to get one to sting you. So, don’t try to catch one in your bare hands. Only the females sting (but males may fake it), because the stinger is derived from the ovipositor, the egg-laying organ. You can distinguish females from males by the curled antennae of the female.
See the Bug guide for more photos.
Pepsis wasps are most active in the summer although they do try to avoid the hottest part of the day. They are found around flowers or on the ground in search of prey. The adult Pepsis wasps feed on nectar and pollen. It is called a tarantula hawk because it hunts tarantulas (and other large spiders) to use in the wasp’s reproductive cycle. The Pepsis wasp will approach a tarantula and cause the spider to rear its legs, thus exposing its abdomen. The wasp will sting the spider to paralyze it. The wasp will lay an egg on the paralyzed spider and drag it to a hole, bury it, and cover up the hole. When the wasp egg hatches, the larvae eats the flesh of the living tarantula for about 35 days, then spins a cocoon and pupates over the winter. If the wasp egg fails to hatch, the spider can recover.
Most predators avoid the Pepsis wasp. However, roadrunners and bullfrogs are known to tackle them.
Recently my wife, Lonni, saw a very large all-black wasp on our back porch. She claimed it was more than four inches long. For some reason she didn’t get a photo. It might have been a large example of Pepsis mexicana (photo below from http://www.arizonensis.org/sonoran/ ).
Videos of Pepsis wasp attacking a tarantula:
Part 1, the attack: http://www.youtube.com/watch?v=5C1wFxEIj8E
Part 2, the kill: http://www.youtube.com/watch?v=D56lxph_WlI