Sharks of Onslow County
On a stroll along the damp sand of the tide line, just after dusk under the soft glow of the moon over Topsail or North Topsail Beach, you might spot a round, glossy shell that looks more like a polished marble than a living creature. This little orb belongs to the Atlantic moon snail or Shark Eye (Neverita duplicata) — smooth and innocent-looking by day, but by night the script flips. It becomes a stealthy predator disguised in plain sight, turning the quiet sand into a midnight hunting ground.
To the casual beachcomber, the moon snail’s shell looks harmless — a perfect spiral polished smooth by the tide. But that rounded shape is built for stealth and movement beneath the sand. Moon snails bury themselves under the flats and inlets of sandy shores, waiting to pounce. Their favorite prey? Soft-bodied bivalves — clams, coquinas, and other shelled animals that live partly buried in sand.
The moon snail doesn’t wait for prey to drift by; it actively hunts. Using its broad, muscular foot, it glides unseen beneath the surface, sensing vibrations of hidden clams. Once it finds a meal, it envelops the prey in its foot like a slow-moving trap — then the drilling begins.
A rough tongue called a radula rasps the surface while secreted acid softens the calcium shell. Hours later, a single round hole opens a doorway to dinner. Every drilled shell that washes up tells the same story. These beveled, countersunk holes are so distinctive that scientists can identify the species of moon snail just by the shape of the bore (Grey & Bounding, 2005; Dietl & Kelley, 2006).
That neat, circular hole — the hallmark of moon snail predation — is what beachcombers often discover without realizing the drama that unfolded beneath their feet.
Unlike many beach creatures you spot on the surface, the moon snail is mostly hidden. During low tide, it may creep near the edge of the exposed flats; at other times, it lies just beneath the surface. When it finds a buried bivalve, it uses a combination of mechanical drilling (via the radula) and acidic secretions to bore through the shell until it can reach the soft tissues inside (Visaggi, Dietl, & Kelley, 2013).
In experimental trials, moon snails were observed to prefer drilling over suffocating their prey, even when the prey was buried at different sediment depths (Visaggi et al., 2013). That means whether the sand is shallow or deeper, the snail still goes for the drill rather than waiting for the prey to weaken.
But that’s not all — stable-isotope studies, which measure chemical fingerprints of diet, show that the moon snail’s feeding habits may be more flexible than once thought. It appears to feed not only on animal prey but occasionally on other resources, hinting at omnivory (Casey, Fall, & Dietl, 2016). In other words: it’s a predator, yes — but one with a backup plan when food runs low.
1. Predator and Prey in One
The moon snail helps regulate bivalve populations, preventing a single species from dominating the sand flats. In doing so, it maintains habitat diversity. At the same time, it transfers energy upward in the food chain by becoming prey for larger predators — fitting neatly into the middle of the coastal food web.
2. Ecosystem Engineer
Burrowing, hunting, and leaving behind drilled shells change the physical landscape of the beach. Each empty shell, each “crime scene” hole, becomes part of the microhabitat for small invertebrates, microbes, and future shell-seekers. In this way, the moon snail contributes to sediment health and biodiversity.
3. The Hidden Drama Beneath Your Feet
From a beachcomber’s perspective, the moon snail is a perfect spooky-season protagonist. Picture it: a “moon” shell glinting under moonlight, a buried assassin beneath your feet, and a perfect little hole in a clam shell — the evidence of a tiny midnight crime.
When a clam is finished, only the perfect circular hole remains — a tiny signature in the sand. Moon snails rarely suffocate their prey; they almost always drill, no matter how deep the clam is buried (Visaggi, Dietl, & Kelley, 2013). This ancient behavior has marked shells for millions of years — the same holes appear in fossils that predate the Carolina coastline.
And when food runs low, the story turns darker. In crowded flats where competition is fierce, moon snails have been observed turning their drills on each other. Cannibalism, rare in most mollusks, becomes a desperate survival strategy in the world beneath the sand (Gould, 2010).
The moon snail’s creeping movements do more than tell tales of horror. Its trails of mucus — left behind as it slides through the sand — subtly transform the beach. That film of slime “primes” the sediment, helping microbes break down organic matter faster and releasing nutrients back into the ecosystem (Hannides & Aller, 2016).
So while it’s a killer to clams, it’s also a quiet caretaker. Its hunting churns the sand, its slime fuels the microbes, and its discarded shells shelter the next wave of tiny life.
Every act of predation keeps the beach in balance. Moon snails are secondary consumers, feeding on clams that filter plankton from the water. In doing so, they prevent any single species from overrunning the flats. And they, in turn, become prey for blue crabs, rays, and drum fish that patrol the shallows.
Each neat hole in a shell is a record of that balance — energy passed from clam to snail to crab to ocean. Nothing wasted. Everything connected.
If you’re exploring the sands of Onslow County — Topsail Island, North Topsail, Surf City, or the New River Inlet — here’s what to watch for:
It’s easy to write off a pretty shell as just another beach find. But every shell, hole, and collar tells a story of life beneath the waves. The moon snail wears the moon’s name well — luminous, secretive, and always working in the dark. Its beauty hides its appetite; its predation hides its purpose.
In its own way, it keeps the beach breathing — a tiny engineer of life and death that turns sand, shell, and shadow into an endless cycle. The next time you find that round shell glinting in the surf, you’re not just finding a souvenir — you’re finding the ghost of a hunter in the sand.
Casey, M. M., Fall, L. M., & Dietl, G. P. (2016). You are what you eat: Stable isotopic evidence indicates that the naticid gastropod Neverita duplicata is an omnivore. Frontiers in Ecology and Evolution, 4, 125. https://doi.org/10.3389/fevo.2016.00125
Dietl, G. O., & Kelley, P. H. (2006). Can naticid gastropod predators be identified by the holes they drill? Ichnos, 13(2), 103–113. https://doi.org/10.1080/10420940600842979
Gould, E. S. (2010). Unexpected rates of cannibalism under competitive conditions by the naticid gastropod Neverita duplicata. Marine Biology, 157(10), 2341–2349. https://doi.org/10.1007/s00227-010-1505-8
Grey, M., & Bounding, E. G. (2005). Shape differences among bore holes drilled by three species of naticid gastropods. Palaeogeography, Palaeoclimatology, Palaeoecology, 221(3–4), 245–260. https://doi.org/10.1016/j.palaeo.2005.02.003
Hannides, A. K., & Aller, R. C. (2016). Priming effect of benthic gastropod mucus on sedimentary organic matter remineralization. Marine Ecology Progress Series, 545, 77–88. https://doi.org/10.3354/meps11587
Visaggi, C. C., Dietl, G. P., & Kelley, P. H. (2013). Testing the influence of sediment depth on drilling behaviour of Neverita duplicata (Gastropoda: Naticidae), with a review of alternative modes of predation by naticids. Journal of Molluscan Studies, 79(4), 310–322. https://doi.org/10.1093/mollus/eyt023
