Tarantula hawks are up to two inches (50mm) long with a red-black body and bright rust-colored wings. The bright rust coloring that they have on their wings is also known as aposematic coloring; this warns its predators that they are dangerous to eat. Their long legs end with hooked claws for grappling with their victims. The stinger of a female tarantula hawk can be up to 1/3 inch (7 mm) long. Their means of reproduction is what gives them their name and fascinates those of us with a morbid curiosity. Females who are ready to lay eggs is on the lookout for a tarantula. They often disturb the web near a tarantulas burrow, and when the tarantula rushes out the wasp stings the spider and injects venom.

The sting, particularly of Pepsis formosa, is among the most painful of any insect. Commenting on his own experience, one researcher described the pain as "...immediate, excruciating pain that simply shuts down one’s ability to do anything, except, perhaps, scream. Mental discipline simply does not work in these situations." It is listed near the top of the list in Schmidt Sting Pain Index. Although the sting is quite painful the effect is reported to last only a few minutes and is fatal less often than the honey bee. Their large stingers are considered defensive adaptations for living in the open, where they are prone to predators.

There are several species of Pompilids, or spider wasps, which are wasps that prey on spiders to feed their young. The tarantula hawk is the largest of these species. It can grow up to four inches in length. The bodies of tarantula hawks are a dark metallic color and their wings are usually bright orange. They are found in the southwestern United States as well as in other arid areas of the world. The adults are nectar feeders and are fond of milkweed.

A female tarantula hawk, once mated and ready to lay eggs, will prey on tarantula spiders. She does this by vibrating the silken strands that lay around a tarantula's hole, enticing it up to the surface. Once the spider is out, the tarantula hawk will sting it with a poisonous venom that causes paralysis, but not death. She then drags the spider to a hole that has been prepared, lays an egg on its abdomen, and seals the hole. In a few days the egg hatches and the larva feeds on the still living tarantula by carefully eating around the spiders vital parts. This keeps the spider alive as long as possible while the tarantula hawk larva continues to feed and grow, eventually metamorphosing into an adult wasp while the spider dies.

Adult tarantula hawks feed on flower nectar or the juice of damaged fruits. Like many other types of wasps, they have a fondness for sweet, oozing, fermented fruit and will behave quite drunkenly after consuming it. Perhaps this explains some of their occasional strange behavior that I’ve observed. More than once I’ve had a tarantula hawk crash into me and fall to the ground and just lay there flailing about. I’ve also seen them do nosedives into the swimming pool for no apparent reason. The wasp shown below was one of the pool divers, and after it was skimmed out of the pool, it wandered around in a daze trying to dry off before finally flying clumsily away.