Quahog Clam

Quick Take

• Quahog clams can actually move, though only for one very specific reason. Their method will surprise you. See how clams walk →
• Every quahog clam starts life as one sex and later becomes another, with size rather than age determining when the switch happens. Explore the sex switch →
• The quahog clam's ancestors survived an extinction event that wiped out over 90% of Earth's species, and something set them apart that made that possible. Trace their survival history →
• Some of the quahog clam's predators have developed surprisingly creative strategies to crack through its defense. Birds are among the craftiest of these predators. Meet the crafty predators →

The quahog clam is an edible marine saltwater invertebrate found primarily along the Atlantic coast of North America. It prefers the shallow inland waters of bays and estuaries. A strong muscle controls their hinged shells, which the clam opens and closes at will. The flesh of these clams is mild, sweet, and briny with a firm texture.

5 Quahog Clam Facts

• Hinged shell: As bivalves, these clams have hinged shells that can open and close. They can also extend their bodies out between the halves, like a tongue.
• Able to “walk”: This remarkable clam can use its muscular “foot” to “walk” across sand or bury itself. It most often walks during the spawning season when it seeks out mates. However, its pace is extremely slow, only 1-2 inches every 15 minutes.
• Popular food source: People around the world value this species for food, to the point that fisheries harvest it commercially.
• Filter-feeders: These clams are omnivores, eating whatever microscopic organisms they can strain or filter out of the surrounding water. They rely on filter-feeding to survive, as they cannot effectively pursue prey.
• Shells made of calcium carbonate: Clam shells are primarily composed of calcium carbonate, a substance also found in rocks, eggshells, and pearls.

Classification and Scientific Name

The scientific name for the quahog clam is Mercenaria mercenaria. Alternate names for this species include the hard clam, northern quahog, hard-shell clam, round clam, and chowder clam. It should not be confused with the ocean quahog (Arctica islandica), which is a type of clam belonging to the family Arcticidae. By contrast, Mercenaria mercenaria belongs to the family Veneridae, the Venus clams. Within this family, it belongs to the genus Mercenaria, which also contains the southern quahog (Mercenaria campechiensis).

In a broader taxonomic sense, the quahog clam belongs to the phylum Mollusca, which contains molluscs or mollusks (soft-bodied invertebrates contained within a hard shell). It further belongs to the class Bivalvia, which comprises mollusks enclosed by a two-part hinged shell (bivalves). This subdivides into the order Venerida, a group of primarily saltwater clams, many of which humans use for food.

Appearance

Quahog clams are soft-bodied invertebrates that protect themselves by means of a hard, rounded shell. Calcium carbonate is the primary material found in the shell, accompanied by a small percentage of other tissues. This thick shell is gray or white in color with concentric growth rings; the inside of the shell is white and violet. Some hatchery clams feature “notata,” dark zigzag stripes across the shell’s exterior.

Inside the shell is the clam’s soft, fleshy body. This body is vulnerable to predation. Two protruding siphons allow these clams to draw water in for filtration and expel the filtered water back into the ocean. Clams of this species have a fairly large shell, ranging from just under 3 inches to 5 inches in diameter.

Evolution and History

The earliest bivalve fossils come from the Early Cambrian Period (541 to 485.4 million years ago), which is the first geologic period of the Paleozoic Era. These tiny organisms belong to the order Fordillida, which has no extant species. To date, scientists have not discovered bivalve fossils from the Middle Cambrian to the Early Ordovician. This was a time of explosive diversity when many organisms were growing in size and expanding into new habitats. Notably, the development of byssal threads in mollusks occurred during the Early Ordovician.

Bivalves became more dominant among marine bottom-dwelling invertebrates after largely surviving the devastating Permian-Triassic extinction event 251.9 million years ago. This event wiped out over 90% of Earth’s species, including many of the rival brachiopods. Throughout the Mesozoic Era, beginning with the Early Triassic, bivalves greatly diversified.

The Cretaceous-Paleogene extinction event, which took place approximately 66 million years ago, destroyed around 65% of bivalve genera. Those that survived are the ancestors of modern bivalves, including quahog clams.

Behavior

The quahog clam spends most of its time buried in the sand, which protects it from predation and the punishing surf. It accomplishes this by expanding and contracting a powerful muscle. It can also use this muscle to “walk” across sediment, typically during spawning season when it seeks out a mate.

This clam is a bivalve, meaning it has a two-part, hinged shell that can open and close at will. A muscle controls the movement of the shell. When feeding, the clam opens its shell and extends its soft body to filter organisms out of the water.

Habitat

Quahog clams are marine animals that require adequate salinity to survive. They inhabit both intertidal and subtidal regions in bays and estuaries, living most of their lives buried in sediment. They typically do not exceed water depths of 118 feet, preferring to remain at 50 feet or above.

These clams occur along the Atlantic coast from Canada’s Gulf of St. Lawrence all the way to Florida. Fisheries have introduced them to countries such as the United Kingdom, France, Belgium, the Netherlands, Puerto Rico, and Taiwan, as well as western U.S. states such as California and Washington.

Eastern states in the U.S. with a quahog clam population include Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas.

Diet, Predators, and Threats

Although quahog clams are mostly sessile, they have adapted to find a way to eat without having to move. Being almost completely immobile, they are also fairly easy targets for predators.

What Eats Quahog Clams?

These clams have a variety of predators, such as fish, crabs, infauna, and birds. Fish predators include angelfish, wrasses, and triggerfish. Crab predators include the blue crab, the green crab, and the mud crab. Lobsters also pose a threat to adult clams. Infauna like worms and snails inhabit soft sediment and may be able to infiltrate a clam’s shell. Additionally, bird species like the American oystercatcher are capable of opening clams and feeding on their insides. Some gulls drop clams from great heights to crack them open.

What Do Quahog Clams Eat?

This species’ diet is limited due to its inability to effectively pursue prey. As a filter-feeder, it mostly consumes phytoplankton, though it also consumes tiny animal organisms such as zooplankton. It does this by pumping water through its body and straining out the desired organisms.

Reproduction and Life Cycle

Quahog clams are protandrous hermaphrodites, beginning life as males and transitioning to females as they grow larger, typically over several years. They reproduce sexually during the spring, early summer, and fall. The males release sperm into the water, which stimulates the females to release eggs. Female clams release anywhere between one and five million eggs while spawning. This may happen several times a year.

Once the eggs are fertilized, embryo development is swift. The eggs hatch after about 12 to 14 hours into trochophores. These microscopic larvae swim using cilia, tiny hair-like projections. After almost 24 hours of development, trochophores enter the veliger stage, during which they acquire wing-like lobes for swimming, a shell, and a muscular foot. This stage lasts six to 10 days, ending in the juvenile stage. At this stage, the clam loses its lobes and settles on the ocean floor, where it will live out the rest of its life.

Sexual maturity for this species depends more upon shell size than age. Some clams mature by the time they reach 1.4 inches in length, though this may not hold for all individuals. This can take between one and two years. A typical lifespan for the species is 12 to 20 years, though some remarkable specimens have lived as long as 40 years.

Population

Though there is no exact data on the quahog clam population worldwide, conservationists do not consider the species to be endangered. Fisheries in the United States currently farm and harvest these animals under sustainable conditions.

The IUCN does not have a listing for this species as of 2026.