Until this weekend, I hadn’t seen mole crabs (Emerita talpoida) since I was a child. The lack of sightings was less to do with an absence of the crabs and more to do with the fact that I no longer dig holes and build sandcastles at the beach. My boyfriend and I were discussing these interesting little crabs as we walked down the beach yesterday and he wanted to see one. My suggestion: dig a hole in the wet sand. It turns out that was really all it took. He quickly unearthed 4 of them in as many tries.

There are a number of species of mole crabs, but the only one found in Massachusetts is Emerita talpoida. Mole crabs, however, are not true crabs.  True crabs have four developed pairs of walking legs, upper shells with points, or teeth, along the margins, and usually a pair of claws. Mole crabs, on the other hand, resemble a grape more than a crab and are classified as an Anomura crab, along with hermit crabs.  Anomura means “differently-tailed”. While all true crabs share some obvious similarities, the various groups of anomurans are quite dissimilar. Mole crabs have three pairs of very short legs, and although some species of mole crabs do have claws, E. talpoida does not. In addition, their tail is also formed into a triangular appendage for digging.

Front (anterior) end of a mole crab, with its eye stalks clearly visible.

This design, while somewhat un-crab-like, is perfect for for burrowing quickly. Mole crabs live in sandy surf zones along coastal beaches, moving up and down the beach with the tides, so they’re constantly subject to wave action. Although this seems like a difficult place to live, it provides the mole crabs with an excellent feeding opportunity. As the waves rush back out, mole crabs extend two feathery antennae through the surface of the sand to collect organic debris floating in the water that rushes over them.

Underside of a female mole crab (anterior end is pointed down in the photo; posterior/tail end is pointed up in the photo); an orange mass of eggs can clearly be seen under the triangular tail.

Mole crab moving along the sand backwards (right to left in the photo), preparing to burrow into the sand.