The wasp provokes a tarantula out of its burrow, avoids the fangs, and delivers a sting to a membrane near the leg base. The venom acts on the spider's nervous system and produces lasting paralysis rather than death. The wasp then hauls a spider many times her own mass to a burrow, seals it in, and lays a single egg on the abdomen.
The larva hatches and feeds through the body wall. It consumes the spider in an order that keeps it alive as long as possible, taking non-essential tissue first and reaching the heart and nervous system only at the end. Fresh meat is the point: a killed spider would decay.
The sting is famous for pain and is placed near the top of Justin Schmidt's sting pain index, described as instantaneous and electric but lasting only a few minutes. Its toxicity to humans is low. Only females sting, since males have no sting, and tarantula hawks do not defend a nest, so encounters are almost entirely a matter of handling one.