A few unlucky planets of the Imperium have to deal with the scourge that is an Arachnospila colony. These strange, four-legged insects live in massive underground hives that are marked by a raised ring of dirt that has been tinged red by a pheromone they secrete. If a hive is disturbed by an invader, they'll angrily pour from their home and swarm the aggressor. Having feeble exoskeletons, Arachnospila possess only one method of attack: dying. When an Arachnospila dies, it explodes in a shower of acid. The explosion of caustic fluid is often enough to kill a man and certainly any creature foolish enough to bumble into a hive's territory.

Due to the fact that Arachnospila multiply at an alarming rate, exterminating them is quite difficult. Larger species have been hinted at, but such reports remain unconfirmed.