Crundles are an enemy creature found in Dwarf Fortress.
Crundles are tiny underground monsters with large claws and horns. They walk on two legs and are dangerous when encountered in large numbers.
While weak individually, crundles often move in large packs and can pose a substantial danger to workers, weavers, and farmers that might be wandering through the underground. However, they tend to scatter when confronted with well-armed soldiers, and so pose little threat to any troops you send to take care of them.
If you rely on traps to defend your fortress, it should be noted that pit traps are fairly ineffective against crundles. They don't hit the ground hard enough. Unless, of course, the ground is made of magma.