If you’ve spent much time at the beach here in Virginia, you’ve almost certainly seen them. As night falls, they emerge, pale under the moonlight. A scuttle of movement, a dash to the water’s edge and away. Startled, they disappear, seemingly vanishing into the sand, only to creep forth once more in a constant dance through the dark hours.
These are Atlantic ghost crabs, aptly named both for their coloring and their nocturnal habits. Land-dwelling crustaceans, they nevertheless remain tethered to the sea, passing their adult lives occupying that ever-shifting borderland where ocean meets shore.
All about the Ghost Crab
Atlantic ghost crabs actually begin their lives in the sea, however. Females lay their eggs in the water, and, once hatched, the young crabs go through several larval stages in the water before coming ashore as tiny crablings. Not surprisingly, this ocean-going interlude is fraught with peril, the larvae being vulnerable to predation and a certain randomness of chance that they’ll find their way back to a hospitable sandy shoreline.
Once back on the beach, though, ghost crabs remain on land for the rest of their short (one to three years, on average) lifespan. There, they dig burrows in the sand, the youngest staying closest to the waterline—in part because it can be quite literally a crab-eat-crab world for this species, with older, larger crabs sometimes preying on their younger, smaller kin. The burrows can reach as much as four feet deep, which is a remarkable act of excavation considering that the adult crabs reach a body size of only about two inches across. Sometimes, if you’re sitting still on a quiet, lightly traveled beach, you might observe a ghost crab tidying its burrow in the daylight hours, sidling out of its tunnel entrance cradling a load of sand in the crook of its front, claw-ended “arms.” Technically actually legs, these “chelipeds” serve both defensive and offensive purposes, their main function being to allow the crabs to pincer and crush their prey, which can include insects and mole crabs but also sea turtle and plover eggs. In fact, research suggests that ghost crab predation may have a meaningful impact on these latter threatened species, although habitat loss is the greater danger to both predator and prey in this case.
Atlantic beaches, of course, have been subject both to overdevelopment and to the growing threat of sea-level rise. And the ghost crab is a true edge species, its survival dependent upon inhabiting the border space of these sandy shorelines. As both predator and scavengers, they live off the ocean edge’s bounty. In addition, though it is perhaps ironically true that ghost crabs will drown if submerged too long in the water, at the same time they also must keep their gills moistened so they can breathe. To this end, they can tiptoe to the surf line to allow the final reach of a wave to wash over them, or even wick up water from damp sand deep in their burrows, via fine hairs on their legs.
Speaking of those legs, it’s the eight unclawed ones that endow ghost crabs with their most effective defense: speed. For a tiny crustacean, a ghost crab can get a move on, fleet-footedly dashing across the sand at speeds up to nine miles per hour and darting in retreat into a subsurface burrow or sometimes simply burying itself in a dusting of sand, into which its coloring blends the crab almost invisibly. (Their speediness has made them a subject of interest for researchers; one study examined their aerobic metabolism by putting the crabs on tiny treadmills.)
All about the Ghost Crab
Another notable feature of the ghost crab is its bendable eyestalks, which can take in a 360-degree view and, of course, are suited for the low light of night. Ghost crabs will occasionally “wipe” their eyestalks with their mouth parts, a neat trick akin to licking your own eyeballs, and oddly entertaining to watch in online videos, proving that there is still something on the internet that isn’t awful.
Spring is a great time to go ghost-crab seeking, when the crustaceans become active but before the beaches are over-run with human visitors. Take your flashlight and your patience to your favorite Virginia beach, and wait quietly in the gathering dusk, watching for the ghosts to rise.
Insatiably curious, Caroline Kettlewell has written on many topics, from endurance athletes and electric cars to Virginia’s delightful natural diversity.
