Crabs are crustaceans belonging to the order Decapoda, with over 6,700 species worldwide. They’re known for their hard exoskeleton, ten legs (including two claws), and side-walking gait. From oceans to forests, crabs have adapted to nearly every environment, showcasing incredible evolutionary variety.
Marine crabs, like the blue crab and king crab, dominate coastal and deep-sea habitats. They feed on fish, mollusks, and detritus, using powerful claws to crush prey. Many are commercially harvested, supporting fisheries and cuisines globally, though overfishing threatens some populations.
Terrestrial crabs, such as the coconut crab and land crab, live on land but often return to water to reproduce. They breathe air through modified gills or lungs and eat plants, insects, or carrion. These crabs thrive in tropical regions, from beaches to jungles.
Freshwater crabs, found in rivers and lakes, skip the marine larval stage typical of many species. They’re smaller, feeding on algae and insects, and play key roles in aquatic ecosystems. Pollution and habitat loss pose significant risks to their survival.
Crabs vary wildly in size and appearance, from the tiny pea crab (under an inch) to the massive Japanese spider crab (12-foot leg span). Colors range from muted browns to vivid reds and blues, often serving as camouflage or mating signals.
Ecologically, crabs are vital scavengers and predators, recycling nutrients and shaping habitats through burrowing. Culturally, they’re food, pets, and symbols—like the zodiac’s Cancer. Their resilience and diversity make them a fascinating group worth studying and protecting.
Types of Crabs
Blue Crab (Callinectes sapidus)
The blue crab is one of the most iconic species, particularly along the Atlantic and Gulf coasts of the United States. Known for its striking blue claws and olive-green carapace, this crab is a strong swimmer thanks to its paddle-like rear legs. Blue crabs thrive in estuaries and coastal waters, feeding on fish, mollusks, and even other crabs. They’re a culinary favorite, especially in dishes like Maryland crab cakes, but their populations are sensitive to overfishing and environmental changes. Males and females can be distinguished by the shape of their abdominal apron—wide and rounded for females, narrow and pointed for males.
Dungeness Crab (Metacarcinus magister)
Found along the Pacific coast of North America, the Dungeness crab is prized for its sweet, tender meat. This species has a reddish-brown carapace that can grow up to 10 inches wide, with powerful claws used for cracking open shellfish. Dungeness crabs inhabit sandy or muddy ocean floors, often at depths of 20 to 100 feet. Named after Dungeness Spit in Washington, they’re a cornerstone of the West Coast seafood industry. Their life cycle includes a larval stage where they drift as plankton before settling as bottom-dwellers, making them vulnerable to ocean currents and predation early on.
King Crab (Paralithodes camtschaticus)
King crabs, particularly the red king crab, are giants of the crab world, with leg spans reaching up to 6 feet and weighing as much as 20 pounds. Native to the cold waters of the Bering Sea and North Pacific, they’re easily recognized by their spiky, reddish shells. Despite their name, they’re not true crabs but belong to a closely related group called lithodids. King crabs are bottom-dwellers, feeding on a variety of organisms like sea stars and worms. Their long legs make them adept at traversing the seafloor, and their meat is a delicacy, often harvested in challenging, icy conditions.
Snow Crab (Chionoecetes opilio)
Snow crabs, also known as opilio crabs, are smaller than king crabs but still commercially significant, especially in the North Atlantic and Pacific. They have long, spindly legs and a light brown to reddish carapace that blends into their snowy, cold-water habitats. Snow crabs prefer depths of 100 to 1,000 feet and feed on detritus, algae, and small invertebrates. Their sweet, delicate meat is a staple in seafood markets, often sold as clusters of legs. Unlike some crabs, snow crabs don’t regenerate lost limbs as efficiently, making predation a bigger threat.
Coconut Crab (Birgus latro)
The coconut crab is the largest terrestrial arthropod, capable of growing up to 3 feet across and weighing over 9 pounds. Found on tropical islands in the Indian and Pacific Oceans, this species is famous for climbing trees to feast on coconuts, which it cracks open with its massive claws. Unlike most crabs, coconut crabs are fully adapted to life on land, with lungs instead of gills, though they still lay eggs in the sea. Their brownish-red bodies and nocturnal habits make them elusive, but they’re a cultural icon in many island communities, despite declining numbers due to habitat loss.
Fiddler Crab (genus Uca)
Fiddler crabs are small, colorful crabs known for the males’ oversized claw, which can be as large as their body. Found in muddy coastal areas and mangroves worldwide, they use this claw to attract mates and fend off rivals in dramatic waving displays. Their carapace is typically under 2 inches wide, and they come in shades of yellow, red, or blue. Fiddler crabs are detritivores, sifting through sediment for organic matter. Their burrowing habits help aerate soil, playing a key role in wetland ecosystems, though they’re vulnerable to pollution and habitat destruction.
Horseshoe Crab (Limulus polyphemus)
Though not a true crab (it’s more closely related to spiders), the horseshoe crab is often included in crab discussions due to its name and appearance. Found along the Atlantic coast of North America, it has a hard, horseshoe-shaped shell and a long, spiky tail called a telson. Horseshoe crabs have remained largely unchanged for over 400 million years, earning them the title of “living fossils.” They feed on worms and mollusks in shallow waters, and their blue blood is harvested for medical testing due to its bacteria-detecting properties, though this practice raises conservation concerns.
Hermit Crab (superfamily Paguroidea)
Hermit crabs are unique for their use of discarded shells as mobile homes, protecting their soft, curved abdomens. Found in marine and terrestrial environments worldwide, they vary widely in size and color. Marine hermit crabs scavenge along ocean floors, while terrestrial species, like those in the Caribbean, live on land but return to the sea to reproduce. They’re omnivores, eating algae, carrion, and small animals. As they grow, hermit crabs must find larger shells, leading to fascinating “housing swaps” in the wild. Their adaptability makes them popular as pets.
Japanese Spider Crab (Macrocheira kaempferi)
The Japanese spider crab holds the record for the largest leg span of any arthropod, reaching up to 12 feet from claw to claw. Native to the Pacific waters around Japan, it has a bulbous, orange-and-white body and spindly legs that make it look otherworldly. These deep-sea crabs live at depths of 500 to 1,000 feet, scavenging for dead fish and plants. Their size deters most predators, though they’re occasionally caught for food or display. Despite their intimidating appearance, they’re gentle giants with a lifespan that can exceed 100 years.
Stone Crab (Menippe mercenaria)
Stone crabs are found in the western Atlantic and Gulf of Mexico, known for their massive, black-tipped claws that can exert crushing force. Their brownish-red bodies blend into rocky or seagrass habitats, where they hunt oysters and other shellfish. Fishermen harvest only their claws, releasing the crabs to regenerate new ones—a sustainable practice if done responsibly. Stone crab meat is a delicacy, often served chilled with mustard sauce. They’re nocturnal and territorial, using their claws for both feeding and defense.
Pea Crab (family Pinnotheridae)
Pea crabs are tiny, often less than an inch wide, and live as commensals or parasites inside bivalves like oysters and mussels. Found worldwide, they have soft, translucent bodies that make them hard to spot. Females typically stay inside their host, feeding on filtered food particles, while males roam more freely. Though they don’t cause significant harm to their hosts, their presence can annoy oyster farmers. Pea crabs are a curious example of symbiosis in the crab world, showcasing how diverse crab lifestyles can be.
Ghost Crab (genus Ocypode)
Ghost crabs are small, fast-moving crabs found on sandy beaches across tropical and subtropical regions. Their pale, sand-colored bodies provide excellent camouflage, and their large, stalked eyes give them a wide field of vision to spot predators. Ghost crabs are nocturnal scavengers, feeding on insects, carrion, and organic debris. They dig deep burrows above the tide line, emerging at night to dart across the shore—hence their “ghostly” name. Their speed and agility make them a challenge to catch, and they’re a vital part of beach ecosystems.
Sally Lightfoot Crab (Grapsus grapsus)
The Sally Lightfoot crab, also known as the red rock crab, is a vibrant species found along rocky coastlines of the Pacific, from Mexico to Chile, including the Galápagos Islands. Its carapace boasts bright red, yellow, and orange hues, making it stand out against dark volcanic rocks. These agile crabs are expert climbers and scurriers, darting away from waves and predators with impressive speed. They feed on algae, small invertebrates, and carrion, using their nimble claws. Their name is said to come from their light-footed agility, resembling a dancer skipping across the shore.
Porcelain Crab (family Porcellanidae)
Porcelain crabs aren’t true crabs but close relatives, distinguished by their flattened bodies and delicate, porcelain-like appearance. Found in tropical and temperate waters worldwide, they often live under rocks or among corals, filtering plankton and detritus with feathery mouthparts. Their carapace is typically less than 2 inches wide, and they’re known for shedding limbs easily when threatened—a trait called autotomy. Unlike true crabs, they have only three pairs of walking legs, with the fourth pair reduced. Their fragility and beauty make them a favorite in marine aquariums.
Mud Crab (Scylla serrata)
Mud crabs, also called mangrove crabs, are large, aggressive crabs found in estuaries and mangroves across the Indo-Pacific region. Their dark green to brown carapace can span up to 9 inches, and their powerful claws make them formidable predators of fish, mollusks, and smaller crabs. Mud crabs are prized in Southeast Asian cuisine, often steamed or stir-fried with spices like black pepper. They burrow into muddy substrates to hide and ambush prey, and their territorial nature makes them a challenge to catch. Aquaculture of mud crabs is growing due to high demand.
Sand Crab (Emerita analoga)
Sand crabs, also known as mole crabs, are small, egg-shaped crustaceans that inhabit sandy beaches along the Pacific and Atlantic coasts. Their smooth, grayish carapace, usually under 2 inches long, is perfectly adapted for burrowing backward into wet sand using their strong legs. They feed by filtering plankton and organic particles from receding waves, positioning themselves with their antennae exposed. Sand crabs are a key food source for shorebirds and fish, and their presence is a sign of a healthy beach ecosystem. Females are larger than males and often carry bright orange eggs.
Velvet Crab (Necora puber)
The velvet crab, native to the northeastern Atlantic and Mediterranean, gets its name from the fine, velvety hairs covering its reddish-brown carapace. Growing up to 4 inches wide, it has a feisty temperament and quick movements, earning it the nickname “devil crab” in some regions. Velvet crabs prefer rocky shores and subtidal zones, where they hunt small fish, worms, and crustaceans with their strong claws. They’re edible and harvested in Europe, though their meat is less popular than that of larger crabs. Their striking blue-tipped claws add a splash of color.
Box Crab (Calappa hepatica)
Box crabs are peculiar deep-sea dwellers found in tropical and subtropical oceans, named for their ability to tuck their legs tightly against their body, resembling a closed box. Their carapace, often mottled with red and white, can reach 6 inches wide, and their oversized claws are specialized for crushing mollusks and hermit crabs. Box crabs live on sandy or muddy seafloors at depths up to 1,000 feet, using their claws like can openers to access prey. Their unique shape and behavior make them a standout among crab species.
Shame-Faced Crab (Calappa granulata)
Another member of the Calappa genus, the shame-faced crab earns its name from the way its claws fold over its face, giving the impression it’s hiding. Found in the Atlantic and Mediterranean, this species has a bumpy, pinkish carapace up to 4 inches wide. Like the box crab, it’s a mollusk specialist, using its robust claws to break open shells. Shame-faced crabs prefer sandy or gravelly bottoms at moderate depths, where they blend in with their surroundings. Their shy appearance belies their predatory prowess.
Arrow Crab (Stenorhynchus seticornis)
The arrow crab, a quirky inhabitant of Caribbean coral reefs, has a triangular, yellow body and long, spider-like legs that can span 6 inches. Its pointed rostrum and thin claws give it an arrowhead shape, perfect for navigating crevices. Arrow crabs are nocturnal scavengers, feeding on algae, small invertebrates, and detritus, often picking food with delicate precision. They’re popular in reef aquariums due to their striking look and pest-control habits, though their fragile legs make them vulnerable to tank mates. They’re more closely related to spider crabs than true crabs.
Green Crab (Carcinus maenas)
The green crab is a small but invasive species, native to Europe but now widespread in North America, Australia, and beyond. Its carapace, typically 3 to 4 inches wide, ranges from green to reddish-brown, depending on its molt cycle. Green crabs are opportunistic feeders, consuming clams, worms, and other crabs, which has made them a threat to native ecosystems. They thrive in intertidal zones and estuaries, tolerating a wide range of salinities and temperatures. Efforts to control their spread continue, as they disrupt shellfish industries and biodiversity.
Masked Crab (Corystes cassivelaunus)
The masked crab, found in the North Atlantic and North Sea, is a small, burrowing species with a carapace under 2 inches wide. Its yellowish-brown body has two antenna-like tubes that form a “mask” over its face, used to breathe while buried in sand. Masked crabs dig into shallow seafloors, feeding on worms and tiny crustaceans they detect with their sensitive antennae. Their camouflaged lifestyle protects them from predators, and they’re rarely seen unless dredged up. Their unique respiratory adaptation is a marvel of evolution.
Hairy Crab (Pilumnus hirtellus)
Hairy crabs are small, bristly creatures found in the Atlantic and Mediterranean, often hiding among rocks or seaweed. Their carapace, about 1 inch wide, is covered in fine hairs that trap sediment, aiding camouflage. These crabs are scavengers and predators, eating algae, detritus, and small invertebrates with their nimble claws. Hairy crabs prefer shallow, rocky habitats where they can blend in, and their hairy exterior makes them look like part of the environment. They’re a subtle but essential part of coastal ecosystems.
Land Crab (family Gecarcinidae)
Land crabs, such as the Caribbean’s black land crab (Gecarcinus ruricola), are fully terrestrial species that live far from the sea, though they return to water to lay eggs. Their carapace can grow up to 4 inches wide, and their colors range from black to bright red or yellow. Land crabs dig burrows in forests or fields, feeding on plants, insects, and carrion. They breathe air through modified gills kept moist by humid environments. In some regions, they’re a seasonal delicacy, but habitat loss threatens their populations.
Red Claw Crab (Perisesarma bidens)
The red claw crab is a small, semi-terrestrial species native to the mangroves and estuaries of the Indo-Pacific, including Southeast Asia. Its carapace, typically under 2 inches wide, is a muted brown or gray, but its vivid red claws make it unmistakable. These crabs are adept climbers, often scaling mangrove roots or rocks, and they feed on algae, detritus, and small invertebrates. Red claw crabs can breathe air through modified gills, allowing them to thrive in both water and humid terrestrial environments. They’re popular in the aquarium trade due to their striking appearance and active nature.
Deep-Sea Red Crab (Chaceon quinquedens)
The deep-sea red crab inhabits the continental slopes of the western Atlantic, from Nova Scotia to the Gulf of Mexico, at depths of 600 to 3,000 feet. Its bright red carapace, which can grow up to 7 inches wide, stands out against the dark seafloor. These crabs are scavengers and predators, feeding on fish, squid, and other deep-sea organisms with their strong claws. Unlike shallow-water crabs, they endure extreme pressure and cold, making them a target for deep-sea fisheries. Their slow growth and late maturity raise concerns about overharvesting.
Freshwater Crab (family Potamidae)
Freshwater crabs, such as those in the Potamidae family, are found in rivers, streams, and lakes across Africa, Asia, and parts of Europe. Unlike their marine cousins, these crabs lack a larval stage in saltwater, completing their life cycle entirely in freshwater. Their carapace varies widely in size and color—often brown or green—and they feed on algae, insects, and organic debris. Species like the Chinese mitten crab (a related freshwater invader) are known for their hairy claws. Freshwater crabs are vital to aquatic ecosystems but face threats from pollution and habitat loss.
Rock Crab (Cancer irroratus)
The rock crab, also called the Atlantic rock crab, is a common sight along the eastern coast of North America, from Labrador to South Carolina. Its carapace, up to 5 inches wide, is yellowish-brown with reddish spots, blending seamlessly with rocky shores and subtidal zones. Rock crabs are opportunistic feeders, cracking open mollusks and scavenging carrion with their sturdy claws. They’re often caught as bycatch in lobster fisheries and are edible, though less prized than other commercial crabs. Their adaptability allows them to thrive in varied coastal habitats.
Spanner Crab (Ranina ranina)
The spanner crab, found in the Indo-Pacific from Australia to Hawaii, has a distinctive, flattened, orange-red carapace that can reach 6 inches wide. Its forward-facing claws resemble spanners (wrenches), hence the name, and are used to dig into sandy ocean floors at depths of 30 to 300 feet. Spanner crabs feed on small fish and invertebrates, ambushing prey from their burrows. They’re a delicacy in Australia, where they’re sustainably harvested using pots. Their unique shape and behavior set them apart from more typical crab forms.
Kelp Crab (Pugettia producta)
Kelp crabs inhabit the Pacific coast of North America, from Alaska to Baja California, living among kelp forests and rocky shores. Their carapace, about 3 to 4 inches wide, ranges from green to brown, matching the seaweed they cling to with their long, slender legs. Kelp crabs are primarily herbivores, grazing on kelp and algae, though they’ll eat small invertebrates if available. Their cryptic coloration and preference for kelp beds provide camouflage from predators like sea otters. They’re a key part of the kelp forest food web.
Soldier Crab (Mictyris longicarpus)
Soldier crabs are small, blue or gray crabs found on sandy beaches and mudflats across the Indo-Pacific, particularly Australia. Their rounded carapace is less than an inch wide, and they move in large, synchronized groups—resembling an army on the march—hence their name. Soldier crabs feed on detritus and microorganisms, filtering food from sand with their mouthparts as they burrow spirally downward. Their mass movements aerate sediment and recycle nutrients, benefiting coastal ecosystems. They’re a striking sight during low tides.
Matuta Crab (family Matutidae)
Matuta crabs, sometimes called moon crabs, are small, colorful species found in shallow tropical waters of the Indo-Pacific. Their carapace, often under 2 inches wide, is rounded and patterned with spots or stripes in shades of yellow, orange, or red. These crabs have paddle-like legs, perfect for digging into sandy bottoms where they hide from predators and ambush prey like small fish and crustaceans. Matuta crabs are nocturnal, emerging under moonlight to hunt, which ties into their common name. Their compact, sturdy build makes them efficient burrowers.