Holes on the Beach

Do you remember when you were a little kid and you maybe loved digging holes at the beach? Perhaps you tried to excavate tunnels or you simply dug a hole in which to bury your feet. What we do to entertain ourselves, animals do for survival.

“What makes all these holes on the beach?”

Within the first week of moving here, my husband and I took a stroll on the beach near Fort Moultrie.  Being January, there weren’t many people walking around, aside from an elderly midwestern couple that was headed towards us.  The fellow stopped when he was withing speaking distance, leaned heavily on his cane, and stated: “You two look like beachwalkers. What makes all these holes?” Still confused as to what of my appearance suggested beachwalker [I had hiking boots on!], I fumbled around for a logical answer. I really had no idea since we had just moved here, but I threw out ‘worms’ as a possibility, to which the gentleman countered “But there’s so many!”

While there are beach worms that make holes, like the lung worm, there is also another hole-loving character–the ghost shrimp.

Ghost shrimp, as well as other shrimp, crabs, and lobsters are crustaceans with ten legs, called decapods. While the ghost shrimp sounds like it would be related to the shrimp you find on your seafood plate, it’s actually more closely related to the American lobster and hermit crabs. They have long bodies, a fanned tail, and usually one claw is extraordinarily larger than the other, white in color, and very smooth, as seen in the photos.

These ‘shrimp’ dig extensive passages under the sand, going as deep as 6 feet below the sand, and pump water through the burrows with their bodies. The water can come out so forcibly it looks like a miniature Old Faithful spewing [see photo right].  Other times, small bits of shells and sand will flow out.  These burrow systems are found near the low tide line, occasionally with fecal pellets deposited outside. It is said that these burrowing crustaceans love their homes so much that they can only survive a few hours without feeling their burrow walls.  Other holes found in the same area with mounds of sand or mud around them are generally worms. 

“Precise Little Holes”

There seems to be a phenomenon on the beach where thousands of beach-goers find perfect little holes in shells but don’t know how they got there.  These holes are generally found on the back-end of bivalves [things like clams, scallops, and the like], but can be found on other gastropods as well. They look like they were drilled there by someone looking to make necklaces out of the shells, but in fact, they were created by another mollusk.

Some sea snails, and in this particular case, the Atlantic moon snail, Polinices duplicatus, also known commonly as Shark’s eye, are carnivorous and actively pursue prey.  They use their very large mantle and foot to encase their food and with their radula bore a beveled hole into shells. A radula in this case is a tongue-like apparatus with many sharp teeth-like projections used to, essentially, lick holes in things.  It isn’t clear if the moon snails suck the prey out of this hole that it creates, or if perhaps because of the positioning of the hole, the abductor muscle of the bivalve releases and allows the shell to open, or maybe due to the acid in the radula, liquification of the bivalve’s muscles occurs. Whatever the case, the snail is a very efficient predator and its handiwork is spread along the beaches of the lowcountry.

Besides the child-dug holes often found scattered across busy summer beaches, there are many other holes that open up to fascinating, under the waves, drama.  Check them out and see what you find!

All photos are taken by the author. The larger versions may be viewed by clicking on them. 

Species information adapted from Seashore Animals of the Southeast.