The carapace is predominantly black and white, with more black than white and the claw is often pink. The key feature is that the tip of the dactyl in Austruca occidentalis comes to a more “normal” point rather than the unique fork found in Cranuca inversa.

As their common name suggests, one of the most obvious behaviours in a fiddler crab colony is claw waving: males wave their one enlarged claw to attract females for mating and to repel intruders from their territory. The massive claw can weigh half a male's body weight and is also used as a weapon.