Halloween is tomorrow, so I thought this would be a good time to do a post on ghost crabs. Ghost crabs! Halloween! Get it? Get it?
On the beach here, up near the base of the dunes, one can find many small (up to a few inches across) round holes in the sand, entrances to burrows leading down out of sight. The tracks that surround them make it clear that these are not the homes of mammals, nor (as my students sometimes guess) are they “snake holes.”
These are actually the burrows of ghost crabs, Ocypode quadrata. They get their name from their pale coloration, ability vanish almost instantly into their holes (“Ocypode” is Greek for “swift foot”), and nocturnal habits. Younger ones dig their burrows closer to the waves, while older ones venture farther back into the dunes. They’re almost completely terrestrial, only going into the water to moisten their gills occasionally and lay their eggs – their larvae are planktonic, drifting in the ocean until they’re ready to return to land as adults.
Despite their reputation as being nocturnal, we sometimes see these guys abroad during the day, and if you’re very lucky you can get between one and its burrow and get a close look at it before it disappears.
Look how cool! Those big black eyes swivel to give it excellent, three-hundred-sixty-degree vision. They’re very impressive-looking, and very different in structure from crabs that spend most of their time in the water. While this guy has four pairs of legs well-suited for walking on sand, the rear pair of legs in ocean-going crabs, such as blue or speckled crabs, is modified into a pair of round flippers for swimming.
Like most crabs, these guys will eat just about anything they can find, and that includes newly-hatched sea turtles. Apparently when the sea turtle patrol folks here on the island are out checking nests they try to run over as many ghost crabs as they can with their golf cart.
Anyway, happy Halloween! Check back tomorrow for photos of the costume I wore to teach in Friday morning. I was a marine invertebrate, but not a crab…