Spiders are among the most important predators of flies. Interestingly, there is one family of flies whose members 'return the favor', so to speak, namely the Acroceridae. Their larvae feed on spiders, rarely as ectoparasite but generally as endoparasite. In the end, the spider is doomed and dies, so these fly larvae are parasitoids. The adult flies have a very recognizable appearance, with a tiny head -whence they are called small-headed flies-, a humped thorax and a charaxteristic dumpy look altogether. Females lay enourmous numbers of eggs that hatch into larva that actively search for a host. The large number of eggs indicates that success rate for the larva is very low.