Crabs live among the boulders and crags on hardscrabble shoreline, and are determined scavengers. Though rarely encountered by mice, any meetings are fraught with danger. Crabs are greedy and will fight with mice for scavenged bits.
In Fall 1152 "Chapter 2 - Shadows Within", Sadie meets with Conrad at his home Calogero. The house is overrun with by a swarm of crabs. Sadie and Conrad manage to kill one each. Sadie is forced to leave Conrad behind and he is ripped to shreds by the crabs and devoured.
In Spring 1126, "The Tale of the Wise Weaver", a mouse known as the Wise weaver persuaded a crab assistance against the predators that threatened it and was able to gain a piece of the crab's shell to use as a shield. After gaining a talon from a Hawk and venom from a Snake, the Weaver strikes down the crab in the spot where it removed a piece of its shell.