They often disturb the web near a tarantulas burrow, and when the tarantula rushes out the wasp stings the spider and injects venom.

Now this is where it gets weird. Instead of killing the tarantula, the venom only causes paralysis. The wasp then drags the tarantula to a burrow, stuffs it down the hole, and then lays her eggs on top of the paralyzed spider. Several days later the eggs hatch, and the larvae feed on the still living tarantula.