Spider crabs are fascinating marine creatures known for their unusual appearance, long legs, and impressive size. Among the many species, a few stand out for their remarkable dimensions and ecological importance. From the giant Japanese spider crab to the smaller but equally intriguing Portly spider crab, these species play vital roles in cleaning the ocean floor and maintaining balance in marine ecosystems. This guide explores the five largest spider crabs in the world, highlighting their size, habitat, and diet.
1. Japanese Spider Crab (Macrocheira kaempferi)
The Japanese spider crab is the largest living arthropod in the world, famous for its astonishing leg span and long lifespan. Native to the waters of Japan, it combines an intimidating appearance with an important ecological role as a scavenger.
Identification
- Scientific name: Macrocheira kaempferi
- Common name: Japanese spider crab
- Distinctive feature: Extremely long, spindly legs resembling a spider
- Body (carapace): Oval-shaped, orange with white spots
- Claws: Strong and elongated, adapted for cracking shells and scavenging
- Notable trait: Can live up to 100 years, making it one of the longest-living crabs
Size Comparison
The Japanese spider crab holds the record as the largest crab species. Its leg span can reach up to 3.7 meters (12 feet), far exceeding the height of an average adult human. While its body (carapace) is relatively small at around 30–40 cm (12–16 inches) wide, the stretched limbs create an extraordinary silhouette. Adults weigh about 16–19 kilograms (35–42 pounds), making them heavy but not as bulky as their span suggests.
Habitat
This species is found in the Pacific Ocean near Japan, particularly around Honshu. They live at depths of 150 to 300 meters (490–980 feet), preferring cold, dark waters. During mating season, they may move into shallower areas. Their deep-sea environment helps protect them from predators and supports their scavenger lifestyle.
Diet
Japanese spider crabs are omnivores and scavengers. Their diet includes:
- Dead fish and marine carrion
- Mollusks such as clams and oysters
- Crustaceans like shrimp or small crabs
- Algae and seaweed
- Decaying organic matter
Their feeding habits make them essential cleaners of the seafloor, recycling nutrients back into the marine ecosystem.
2. European Spider Crab (Maja squinado)
The European spider crab is one of the largest crab species in the Atlantic and Mediterranean waters. Recognizable by its spiny shell and powerful legs, it is highly valued both ecologically and commercially. Unlike the Japanese spider crab, it is more compact but still impressive in size.
Identification
- Scientific name: Maja squinado
- Common name: European spider crab
- Distinctive feature: Triangular, spiny carapace with a reddish-brown color
- Claws: Strong but shorter compared to leg length
- Notable trait: Known for seasonal migrations in large groups
Size Comparison
The European spider crab reaches a carapace width of up to 20–25 cm (8–10 inches). Its legs extend the overall size, though not as extreme as the Japanese species. Adult crabs can weigh up to 3 kilograms (6.6 pounds), making them one of the largest crabs in European waters. Compared to humans, they are medium-sized but still striking when seen underwater.
Habitat
This crab inhabits the northeast Atlantic Ocean and Mediterranean Sea, often found along rocky coasts, sandy bottoms, and seagrass beds. They usually live at depths of 5 to 50 meters, but some can be found deeper. Seasonal migrations lead them to travel long distances in large aggregations, making them unique among spider crabs.
Diet
European spider crabs are omnivorous, feeding on:
- Algae and seaweed
- Mollusks such as mussels and clams
- Worms and small crustaceans
- Detritus and decaying matter
Their broad diet supports their survival in diverse habitats and plays an important role in maintaining coastal ecosystem balance.
3. Spiny Spider Crab (Maja crispata)
The Spiny spider crab is a medium-to-large species found mainly in the Mediterranean and parts of the eastern Atlantic Ocean. It is easily recognized by the spiny projections covering its carapace, which provide camouflage and protection. Though not as massive as the Japanese or European spider crabs, it remains a notable member of the spider crab family.
Identification
- Scientific name: Maja crispata
- Common name: Spiny spider crab
- Distinctive feature: Carapace covered with sharp spines and tubercles
- Coloration: Brown to reddish, often encrusted with algae for camouflage
- Claws: Relatively small compared to body size
- Notable trait: Masters of disguise, often blending into rocky or algae-covered habitats
Size Comparison
The Spiny spider crab has a carapace width of 10–12 cm (4–5 inches) on average, with some individuals growing larger. Its long legs extend its reach, making it appear bigger than the carapace suggests. While much smaller than the Japanese spider crab, it is still considered one of the larger crabs within Mediterranean waters.
Habitat
This species thrives in the Mediterranean Sea and eastern Atlantic coastlines, usually in shallow rocky or sandy areas. They are commonly found at depths of 5 to 50 meters, often concealed among algae, rocks, and seagrass beds. Their camouflage ability helps them avoid predators while waiting to scavenge food.
Diet
Spiny spider crabs are omnivores and scavengers. Their diet includes:
- Small mollusks
- Worms and small crustaceans
- Algae and seaweed
- Detritus and decomposing organic matter
This flexible diet makes them adaptable to different marine environments, allowing them to thrive in coastal ecosystems.
4. Common Spider Crab (Maja brachydactyla)
The Common spider crab is a well-known species along the northeastern Atlantic coast, especially around Europe. It resembles the European spider crab but is considered a separate species with distinct features. This crab is often spotted in shallow waters and is recognized for its spiny shell and seasonal group migrations.
Identification
- Scientific name: Maja brachydactyla
- Common name: Common spider crab
- Distinctive feature: Triangular, spiny carapace with curved lateral spines
- Coloration: Brownish-red with algae and barnacle encrustations for camouflage
- Claws: Relatively short but strong, used for breaking shells
- Notable trait: Forms large migrating groups along coastlines
Size Comparison
The Common spider crab reaches a carapace width of up to 20 cm (8 inches), with long legs extending its overall size. Adults can weigh between 1.5 to 3 kilograms (3–6.5 pounds). Though not as enormous as the Japanese spider crab, it remains one of the largest native crabs in European coastal waters.
Habitat
This species inhabits the northeast Atlantic Ocean, particularly along the coasts of France, Spain, Portugal, and the British Isles. They prefer rocky seabeds and seagrass meadows at depths of 5 to 50 meters. During summer, they migrate in large groups to shallower areas, a behavior that makes them highly visible to divers and fishermen.
Diet
Common spider crabs are omnivorous scavengers, consuming:
- Mollusks such as mussels and clams
- Small crustaceans
- Algae and seaweed
- Dead fish and marine carrion
- Organic detritus
Their broad diet supports both survival and ecological balance, as they act as cleaners of the seafloor.
5. Portly Spider Crab (Libinia emarginata)
The Portly spider crab is a North American species commonly found along the Atlantic coast of the United States. Known for its rounded carapace and spiny texture, it is smaller than its Japanese and European relatives but still one of the largest spider crabs in its region. Its unique appearance and scavenger habits make it an important species in coastal ecosystems.
Identification
- Scientific name: Libinia emarginata
- Common name: Portly spider crab
- Distinctive feature: Round, spiny carapace with a rough surface
- Coloration: Brown to gray, often covered with algae or debris for camouflage
- Claws: Short but sturdy, adapted for grasping food
- Notable trait: Known for covering its shell with sponges and algae to hide from predators
Size Comparison
The Portly spider crab is smaller than most of its global relatives but still notable. Its carapace width reaches up to 11 cm (4–4.5 inches), and with extended legs, it can span around 30 cm (12 inches). While it doesn’t compare to the Japanese spider crab’s massive size, it is relatively large among North American crabs.
Habitat
This species is native to the western Atlantic Ocean, particularly along the U.S. East Coast from New England to the Gulf of Mexico. It inhabits shallow waters, often less than 160 feet (50 meters) deep, favoring sandy or muddy bottoms and eelgrass beds.
Diet
The Portly spider crab feeds as a scavenger and omnivore, consuming:
- Dead fish and marine carrion
- Small mollusks and crustaceans
- Worms and soft-bodied invertebrates
- Algae and plant matter
- Organic debris from the seafloor
Its diet supports its role as a natural recycler, keeping coastal waters clean and balanced.
Size Comparison Table
| Species | Carapace Width | Leg Span | Weight | Habitat Range |
| Japanese Spider Crab (Macrocheira kaempferi) | 30–40 cm (12–16 in) | Up to 3.7 m (12 ft) | 16–19 kg (35–42 lbs) | Deep waters of Japan (150–300 m) |
| European Spider Crab (Maja squinado) | 20–25 cm (8–10 in) | ~80 cm (31 in) | Up to 3 kg (6.6 lbs) | Northeast Atlantic & Mediterranean |
| Spiny Spider Crab (Maja crispata) | 10–12 cm (4–5 in) | ~40 cm (16 in) | ~1 kg (2.2 lbs) | Mediterranean & Eastern Atlantic |
| Common Spider Crab (Maja brachydactyla) | Up to 20 cm (8 in) | ~60 cm (24 in) | 1.5–3 kg (3–6.5 lbs) | Northeast Atlantic (France, Spain, Portugal, UK) |
| Portly Spider Crab (Libinia emarginata) | Up to 11 cm (4–4.5 in) | ~30 cm (12 in) | <1 kg (under 2 lbs) | Western Atlantic (U.S. East Coast to Gulf of Mexico) |
