The Dive Shack Tides: Creature Feature: Shame-Faced Crab

The shame-faced crab (aka box crab) gets its name from the way its claws (or chelae) cover its face as if it were trying to hide in shame. Classified in the genus calappa, what distinguishes these crabs from others is their distinctly bulky carapace (upper portion of the shell) which can reach lengths up to 3.5 inches and widths of nearly 5 inches. The calappa species became labeled box crabs because when threatened these crabs pull their large pincers tight around their bodies, hiding their legs under the canopy of their carapace, forming a well-armored “box”.

The shame-faced crab’s squat, rounded and convex shell may be a rosy or yellowish hue with grooves and/or spots on it. The triangular mouth, as well as its eyes, are generally hidden behind the large forceps of its first pair of walking legs. In some species the impression of shame is further enhanced by large reddish-pink spots on the pincers which make the crab look even further embarrassed. The other pairs of legs are rather skinny since they are rarely used.

The shame-faced crab generally remains in an inactive state, burrowed in the sand, eyes looking upward, waiting for potential prey to come by. It can remain in this position for several days, with only its eyes, antennae and upper carapace protruding from the sand. Its forceps also protrude to form a “breathing cave” behind them, preventing sand from blocking its air passages. On the occasion that it does choose to run, it puts its body completely upright and straightens its legs. To bury its self again, it simply pushes its forceps against the sand like planks which then forces its body backward into its burrow.

This crab’s favorite snacks are oysters, mollusks, snails, and other marine invertebrates. Its specially formed forceps and right pincer are well-adapted to pick its prey apart, and strong enough to crack their shells. There is a large accessory tooth at the base of the moveable finger and a corresponding flat plate on the fixed finger which act like a vice to crack through the shell. The left pincer is relatively longer and sharper and used to extract the gastropod’s body from the broken shell. This guy below in the video doesn't accomplish his task with lightening speed, but watch as he goes about getting some dinner.