American Lobster (Homarus americanus): Facts and Size

What does an American lobster look like?

An American lobster has a hard outer skeleton, or exoskeleton, divided into two main parts. The head and thorax are covered by one large shield called the carapace, and behind it is a long, muscular abdomen, usually called the tail, which ends in a wide tail fan. Under the tail are small paired limbs called swimmerets.

Like all decapods (“ten feet”), it has five pairs of legs. The first pair carries the famous claws, and they are not the same. The crusher claw is heavy and blunt, with rounded knobs like molars for cracking shells. The cutter claw, also called the pincer or ripper, is slimmer and has sharp, fine teeth for holding and tearing soft food. Whether the crusher sits on the left or the right makes a lobster “left-handed” or “right-handed”. The next two pairs of legs also end in small pincers, which help the lobster pick up food.

On the head are two long antennae used for touch and two shorter, forked antennules that work as a nose. The eyes sit on movable stalks.

Live American lobsters are not red. Most are olive green to greenish brown, often speckled with orange, red or black, with bluish joints, red spines and an orange-red underside to the claws. The red color appears only after cooking. A tiny fraction are born blue, yellow, orange or even white; you can read why in why are some lobsters blue?

Males and females can be told apart by the first pair of swimmerets, which are hard and grooved in males but soft and thin in females. Females have a broader tail for carrying eggs, and adult males tend to have bigger claws.

How big is an American lobster?

The American lobster is the heaviest crustacean known and, together with the eastern rock lobster of Australia and New Zealand, the longest decapod.

Lobsters sold in markets usually weigh 0.5–1 kg (1–2 lb). Giants of 9 kg (20 lb) or more are rare and usually come from deeper offshore waters. For records and growth rates, see how big do lobsters get?

Habitat and range

American lobsters live along the Atlantic coast of North America from Labrador and Newfoundland south to Cape Hatteras, North Carolina. They are most common in coastal waters from Maine to New Jersey and become scarce farther south. Offshore, they are found along the outer continental shelf to depths of about 700 m (2,300 ft), especially near underwater canyons.

Most live at depths of about 4–50 m (13–164 ft) on rocky bottoms with plenty of cracks and holes to hide in. Young lobsters settle among cobbles, and adults also use boulder fields, eelgrass beds and muddy bottoms where they can dig burrows. They prefer cold water; bottom water warmer than about 20 °C (68 °F) causes stress.

Small lobsters near the coast move very little, but large ones can travel far. Offshore lobsters make spring migrations of about 80–300 km (50–190 mi) toward shallower water. Outside its native range, American lobsters imported live to Europe have occasionally escaped or been released, and some have been caught off Norway, Sweden and Britain, where scientists worry about disease and hybrids with the native European lobster.

What do American lobsters eat?

American lobsters are omnivores and opportunists. Studies of their stomach contents show a diet dominated by mollusks such as mussels, clams and snails, along with sea urchins, sea stars, brittle stars and marine worms. They also eat crabs, small fish, algae and eelgrass, and they scavenge dead animals on the seabed.

Lobsters find food mainly by smell. The antennules pick up odors from a distance, while sensory hairs on the walking legs and mouthparts “taste” anything they touch. The crusher claw cracks shells, and the cutter tears the soft flesh inside.

After molting, a lobster often eats its own discarded shell, which helps it recover calcium for the new one. Lobsters will eat each other when crowded in tanks, and researchers in Maine reported cannibalism among wild lobsters for the first time in 2012. Tiny lobster larvae feed on plankton during their first weeks.

Behavior and senses

American lobsters are solitary, territorial and mostly nocturnal. By day each one hides in a den, a crevice or a burrow it has dug, and it comes out at night to forage. Neighbors sort out a pecking order through claw displays and short fights, and the dominant lobster gets the best shelter.

Much of lobster communication is chemical. Lobsters release urine from openings near the base of the antennae and can squirt it in a plume 1–2 m (3–7 ft) ahead of them when they meet a rival or a mate. Individuals appear to recognize each other by these scents and remember a lost fight for up to about two weeks.

Lobster eyes are built differently from ours. Each compound eye has thousands of square tubes that act like tiny mirrors, focusing light from many units onto the retina. These eyes are good at spotting movement in dim light but do not form sharp images. When threatened, a lobster flips its tail hard and shoots backward through the water.

How lobsters molt and grow

Because its shell cannot stretch, a lobster grows by molting. Before a molt it absorbs some minerals from the old shell and forms a soft new one underneath. The old shell splits between the carapace and the tail, and the lobster pulls itself out backward, then takes in water to swell to its new size. The soft new shell takes weeks to harden fully, and during that time the lobster stays hidden.

Young lobsters molt about ten times in their first year. They molt about 20–25 times over 5–8 years before reaching roughly 0.45 kg (1 lb), the size at which most can breed and be legally caught. After that, a lobster molts about once a year, and large adults only every few years. Each molt can add 40–50% to its weight and about 14% to the length of its carapace. Molting also lets a lobster regrow lost legs and claws.

Laboratory studies in the 1980s showed that which claw becomes the crusher is decided early in life. Juveniles that use their claws to grip and handle objects during a critical stage develop one crusher; those raised with nothing to grasp develop two cutters.

Reproduction and life cycle

Mating takes place soon after a female molts, while her shell is still soft. She chooses a dominant male, moves into his den and releases scents in her urine that make him less aggressive. After her molt, the male transfers a sperm packet, which she can store for a year or more.

When she spawns, the eggs are fertilized as they are released and glued to her swimmerets. Depending on her size, a female carries from about 5,000 to more than 100,000 eggs. She keeps them clean and fanned with water for 9–11 months; a female carrying eggs is said to be “berried”. In New England, eggs are usually laid in July or August and hatch the following May or June.

The larvae drift near the surface and molt three times in their first few weeks. At the fourth stage, about 13 mm (1/2 in) long, they look like tiny adults and soon settle on the bottom. Only about one larva in 1,000 is thought to survive to this point. Females usually mature at about 5–8 years old; lobsters in warmer southern waters grow faster and mature at a smaller size.

How long do American lobsters live?

No one knows exactly. Lobsters shed their entire shell when they molt, so they keep no permanent growth rings like a tree or a clam. NOAA Fisheries says some American lobsters may live to be about 100 years old, while other scientists put the oldest at several decades.

Scientists estimate age from growth models, from an “age pigment” called lipofuscin that builds up in nerve tissue, and, more recently, from growth bands found in the hard teeth of the stomach. Lobsters also produce telomerase, an enzyme linked to cell repair, throughout their lives. That does not make them immortal, as explained in do lobsters live forever?, but it puts them among the longest-living animals in the ocean.

Predators, disease and warming seas

Lobsters are most at risk when young. Larvae are eaten by fish and other plankton feeders, and juveniles are taken by cod, sculpins, flounder, eels, crabs, octopuses, skates, rays and sharks. Seals also eat lobsters. A large lobster with a hard shell has few natural enemies, so people are the main predator of adults.

Warming water is changing where lobsters thrive. The Gulf of Maine is one of the fastest-warming parts of the world’s oceans. As waters warmed from the 1990s, catches in Maine and Atlantic Canada climbed to record levels, while the population off southern New England collapsed. Warm, low-oxygen conditions and disease were linked to mass die-offs in western Long Island Sound in 1999 and 2002, and a bacterial infection called epizootic shell disease, which eats black pits into the shell, has become common in the warmer southern part of the range.

Conservation status

The IUCN Red List classifies the American lobster as Least Concern (assessed in 2011). The species remains abundant over much of its range, especially in the cold northern waters of the Gulf of Maine and Atlantic Canada.

The picture differs by region. According to the 2025 stock assessment by the Atlantic States Marine Fisheries Commission, the Southern New England stock is severely depleted, while the Gulf of Maine and Georges Bank stock is not overfished but is being fished at too high a rate. Rules in the United States and Canada include minimum and maximum sizes and the release of egg-bearing females. In Maine and some other areas, such females are also marked with a V-shaped notch in the tail, which keeps them protected for years after their eggs hatch.

It is also one of North America’s most valuable seafoods and Canada’s top seafood export.

Myths and facts

Myth: lobsters are red. Live American lobsters are greenish brown. Their red pigment, astaxanthin, is bound to proteins in the shell and is released by the heat of cooking.

Myth: lobsters mate for life. They do not. A female stays with a male in his den for a few days to about two weeks around her molt, then leaves, and a dominant male may mate with several females in a season.

Myth: lobsters live forever. They keep growing and show few obvious signs of aging, but they die from molting problems, disease, predators and fishing.

Partly true: lobster was once poor people’s food. In colonial New England, lobsters were so plentiful that they were used as fertilizer and bait and were widely considered cheap food. The popular story that servants had contracts limiting how often they could be served lobster, however, is not backed by any contract historians have found.

Fact: scientists take lobster welfare seriously. A 2021 review for the UK government found strong evidence that decapod crustaceans such as lobsters and crabs are sentient, able to feel pain, and the UK’s Animal Welfare (Sentience) Act 2022 now includes them. To see how lobsters differ from their round-bodied cousins, read crab vs lobster.