You may think I am crazy about predators and parasitoids, but I am not, particularly. I just think they are cool and important parts of their ecosystems. The way parasitoids make their living is unusual, but there is actually a pretty fair number of these species. Flies of the family Tachinidae are parasitoids, as are essentially all members of the wasp families Ichneumonidae (about 60,000 described species) and Braconidae (12,000 described species, with estimates of 50,000 to 150,000 species total). The subject of this post is the family Pompilidae (spider wasps), which includes a group of species referred to as tarantula hawks (genera Pepsis and Hemipepsis).
Tarantulas are obviously large, relatively primitive spiders. The terrestrial species (which we have in north Texas, and for that matter throughout North America) live in burrows in the ground, which they line with spun silk. Tarantulas themselves are predators, and capture crickets and other small arthropods, although some of the larger species in the Neotropics can capture small vertebrates. The tarantulas in the US are essentially harmless to people (although they can be scary) - they can be picked up and handled carefully; some species are kept as pets. One of my office mates in graduate school had one that he kept in our office, and he would occasionally take it out of its terrarium and let it walk around on his arms. There is not much in biology that gives me the willies, but that did.
Tarantula hawks are often relatively large wasps (up to 2 inches), heavy-bodied, with dark bodies and smoky, reddish-orange wings. Tarantula hawks are called that because the females hunt tarantulas to provide for their larvae. You will see them flying slowly a couple of feet above the ground surface, in a pattern that almost seems methodical. They probably find tarantulas using vision more than hearing or smell - it is not uncommon to find tarantulas out and about during the day, although they are primarily nocturnal. When a tarantula hawk finds a tarantula, it stings it to paralyze the tarantula, in much the same way that cicada killers paralyze cicadas.
The tarantula hawk next drags the tarantula to a burrow. There are conflicting reports about this - some say the tarantula hawk digs a burrow in which to place the tarantula, others say the tarantula hawk places the tarantula into the tarantula’s own burrow, which would seem to be the height of adding insult to injury. My guess is that, as Forrest Gump says, it is probably some of both - an individual tarantula hawk probably sometimes digs a burrow, and sometimes uses the tarantula’s burrow.
The tarantula hawk (females only) lays an egg on the body of the tarantula. The egg hatches into a larva, which bores into the tarantula’s body, consuming the internal organs, eventually killing the tarantula and pupating. The pupa ecloses as an adult wasp, starting the life cycle over.