What seemingly cute, small creature is, in fact, a terrifying killer that drills a hole into their prey, liquifies it, and then sucks it out like a smoothie?
The moon snail (Naticidae)!
Have you ever noticed those shells at the beach with perfectly round holes in them? I’ve always wondered how they end up like that. I thought, “surely it is not a coincidence that jewelry-ready shells are left in the sand for a craft-lover like me.” Amazingly, the neat holes are the work of the moon snail.
The Small Snowplows of the Ocean
The moon snail is a predatory sea snail from the Naticidae family, named for the half-moon shaped opening on the underside of its globular shell. They are smooth and shiny and come in a variety of colors and patterns depending on the species: white, gray, brown, blue, or orange, with different spiral bands or waves. The size of moon snails also varies by species, ranging from as small as a marble to as large as a baseball. To traverse the ocean floor, moon snails use a big, fleshy foot to burrow through the sand. They pump water into the foot’s hollow sinuses to expand it in front of and over the shell, making it easier to travel along the ocean floor, like a snowplow. (Or should we call it a sand plow?)
Moon snails live in various saltwater habitats along the coast of North America. A diversity of species can be found along both the Atlantic Coast between Canada down to North Carolina, and the Pacific Coast from British Columbia down to Baja California, Mexico. They live on silty, sandy substrates at a variety of depths depending on the species, from the intertidal zone and shallow waters below the tidemark to muddy bottoms off the coast 500 meters deep (about 1640 feet, which is greater than the height of the Empire State Building!). You might find a moon snail during a full moon, when the tide is higher and more seashells wash up on shore, plowing through the sand looking for its next meal.
When a moon snail fills its muscular foot with water, it can almost cover its entire shell!
The moon snail is part of a taxonomic class called Gastropoda, which describes a group of animals that includes snails, slugs, and nudibranchs. The word gastropod comes from Greek and translates to “stomach foot.” The moon snail is a part of this belly-crawler club because it has a foot that runs along the underside of its belly that it uses to get around!
What’s on the menu? Clam chowder!
What does the moon snail eat? These ocean invertebrates prey primarily on other mollusks that share their habitat, like clams and mussels. They use chemoreception (a process by which organisms respond to chemical stimuli in their environment) to locate a mollusk and envelop it in their inflated foot, dragging it farther into the sand.
Nearly all gastropods have a radula (think of a tongue with a lot of tiny, sharp teeth) that they use to consume smaller pieces of food or scrape algae off rocks. Moon snails are different. After their prey is captured, moon snails use their radula to grind away at a spot on their prey’s shell. With the help of enzymes and acids secreted from glands on the bottom of their foot, they drill completely through the shell of their victim at a rate of half a millimeter per day. Once the drilling is complete, moon snails inject digestive fluids into the mollusk, liquefying its innards, and slurp up the chowder inside with their tubular proboscis. The entire process takes about four to five days. Vicious, right? And what is even more brutal is that sometimes, moon snails are cannibalistic!
What role does the moon snail play in its environment?
Phytoplankton and algae form the foundation of the marine food web, providing food and energy to the entire ecosystem of sea creatures. Organisms that fall prey to moon snails, like clams and mussels, consume this microscopic algae, as well as other bacteria and plant detritus. The moon snail is a vital link in this interconnected food chain because not only is it important prey for predators like crabs, lobsters, and shorebirds, but it also provides these organisms with energy and key nutrients. Through decomposition, moon snails’ feces, dead bodies, and shells become nutrients for producers like phytoplankton and algae.
Unfortunately, many things can harm moon snails and their habitats. Meteorological events like hurricanes can cause fluctuations in the species’ abundance. During heatwaves, when record high temperatures combine with extreme low tides like the one in the Pacific Northwest in 2021, moon snails can become extended from their shells, leading to desiccation and death.
The Earth’s temperature has risen at a rate of approximately 0.2°C per decade since 1982, making 2023 the warmest year since global records began in 1850. If yearly greenhouse gas emissions continue to rapidly increase, the global temperature will be at least 5 degrees Fahrenheit warmer and possibly as much as 10.2 degrees warmer by 2100. This continuous increase in temperature puts not just moon snails but humans and the Earth’s biodiversity at large at risk, not only because of more frequent heat waves, but because oceans are becoming more acidic as the water absorbs excess carbon dioxide from the atmosphere. As reporter Hari Sreenivasan explained in the PBS NewsHour report, Acidifying Waters Corrode Northwest Shellfish, ocean acidification affects shellfish a lot like how osteoporosis causes bones to become brittle in humans. The increasing acidity in the ocean reduces the amount of carbonate in the seawater, making it more difficult for moon snails and other shellfish to build and maintain strong calcium carbonate shells.
Human activities also threaten marine creatures like moon snails. Shoreline hardening, aquaculture operations, and water management disturbs the food web and drives species towards extinction. Building structures on the shore to protect against erosion, storm surge, and sea level rise; projects such as geoduck farming; and creating dams and other water diversions disrupts animal communities and results in considerable habitat change. Fortunately, there are environmentally friendly alternatives, like living shorelines. These use plants and other natural features like rocks and shells to stabilize sediments, absorb wave energy, and protect against erosion.
What can you do to protect these clam-chowing sand plows and the biodiversity of the marine sediment?
One thing you can do to help moon snails is protect their egg casings. In the summer, more moon snails emerge in the shallow, intertidal habitats because it’s time for them to breed. To lay eggs, the female moon snail covers her entire foot in a thick layer of sand that she cements together with mucus. After laying tiny eggs on top, she sandwiches them between another layer of sand and detaches herself from the firm, gelatinous egg mass and leaves them to hatch in a few weeks. These collar-shaped egg casings can sometimes look like pieces of plastic or trash, so make sure you don’t pick them up and throw them away!
Moon snails can be found washed up on dry parts of the beach as well as in submerged parts of sand flats during low tide. If you pick up a moon snail, remember to put it back in the water so it doesn’t dry out in the sun.
The biodiversity in the marine sediment rivals even coral reefs and tropical rainforests. The organisms that live in this part of the ocean and the services they provide are essential for life on Earth. They cycle nutrients, break down pollutants, filter water, and feed commercial species like cod and scallop that humans eat all the time. Historical fishing activities, bottom trawling, habitat destruction, pollution, climate change, food web modification, and invasive species threaten biodiversity, functions, and services of marine sedimentary habitats. While there are many unknowns and ongoing threats to ocean life, that also means there are more opportunities for research and discovery that can inform effective ocean conservation policies. Supporting these policies that protect oceans and marine life is a way to protect moon snails too.
In ecology, there is a principle that suggests that each ecological niche is occupied by a distinct organism uniquely suited to it. This means organisms exist everywhere, and they have evolved to exist in these places in specific ways. The moon snail’s unique characteristics – notably the way it uses its radula to drill into its prey – shows us that in almost any niche, the organism which occupies it has similarly adapted to optimize its place in that habitat. I’m curious to learn what other unique traits organisms have evolved to adapt to their unique niche.
Off to shell-ebrate the beauty of our oceans and their creatures,
Abigail
Abigail Gipson is an environmental advocate with a bachelor’s degree in humanitarian studies from Fordham University. Working to protect the natural world and its inhabitants, Abigail is specifically interested in environmental protection, ecosystem-based adaptation, and the intersection of climate change with human rights and animal welfare. She loves autumn, reading, and gardening.
Sources and Further Reading:
Conservation Organizations
Articles & Papers
- How seashells are made, The Woods Hole Oceanographic Institution
- Impacts from the Summer 2021 Heatwave on Washington Shellfish, University of Washington, 2021
- Scientists seek to untangle ecological effects of water management, Blaine Friedlander, 2018
- Moon Snails Family Naticidae, iNaturalist
- Climate Change: Global Temperature, Rebecca Lindsey AND LuAnn Dahlman 2024
- This is not trash! Moon Snail Egg Collars on the Beach, Judy Drew Fairchild
- How are seashells made?, Woods Hole Oceanographic Institution
- Aquatic food webs, NOAA
- What are phytoplankton?, NOAA
- What Do Clams Eat?, Nikki Dix, et al. 2010
- Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report, Wuebbles, D.J., et al. 2017
- 6.2.1: Competitive exclusion principle, Karen Moody and Al Gonzalez
- Cannibalistic mollusk: The secret life of the northern moon snail, Tarini Fernando, 2023
- Puget Sound sediments, Washington State Department of Ecology