Tarantula Killer is also known as Tarantula Hawk.
It is a large wasp, which captures tarantulas and places them in its nest as food for its young. The spider is paralyzed by a sting. A female wasp finds tarantulas by smell.
Male wasps spend their time perched on tall vegetation looking for females.
I took this photo in Pine Creek area of Red Rocks, Nevada in September 2007.
There are two species of these wasps living in the southwestern US. They are Pepsis formosa and Pepsis thisbe. The two species are difficult to distinguish.
Because of their stingers, very few animals are able to capture and eat Tarantula Killers with the exception of the Roadrunner of course.