Swarm of Stonebreaker Spiders
The stonebreaker is a small spider, not more than 2cm in length at adulthood, with grey-brown mottled carapace and two sets of mandibles. The stonebreaker lives in colonies burrowed deep inside rock, stone and old masonry. Colonies are recognizable by extensive criss-crossing spider webs that protrude from porous holes in the stone, which alert the spiders to prey entering the area.
When hunting stonebreakers attack as a single unit, dozens of spiders swarming the prey and covering it in dozens of tiny bites which can cause petrification. When their prey turns to stone, the spiders will enter a frenzy and begin rapidly consuming the hapless creature, first breaking it into large chunks and then into ever-smaller pieces to be carried back into the colony.
When attacked, the swarm instinctively recoils and retreats back into its lair when possible, but will re-emerge seconds later so long as prey is available.