AT A GLANCE
- Common Name: European Spider Crab
- Scientific Name: Maja squinado
- Category: Invertebrates
- Subcategory: Crustaceans
- Range: Northeastern Atlantic Ocean and the Mediterranean Sea, from the British Isles and Ireland south to Mauritania
- Habitat Type: Subtidal rocky reefs, sandy bottoms, kelp forests, and gravelly substrates from the lower shore down to 150 meters depth
- IUCN Red List Status: Not Evaluated (assessed locally as Stable / Least Concern)
- Lifespan: 5 to 8 years
- Diet: Omnivorous/Opportunistic scavenger (algae, mollusks, echinoderms, polychaete worms, and carrion)
- Average Size/Weight: Carapace length up to 20 cm; leg span up to 50 cm; weight up to 2.5 kg
- Key Defining Feature: Heart-shaped, heavily spined reddish-brown carapace with exceptionally long, spidery walking legs and small chelae
Overview
The European Spider Crab (Maja squinado) is a large, iconic marine decapod crustacean inhabiting the temperate and warm-temperate waters of the northeastern Atlantic Ocean and Mediterranean Sea. Known for its heavily armored, thorn-covered carapace and long, gangly walking legs, it is a dominant benthic omnivore of subtidal reefs and kelp forests. Spider crabs are famous for their seasonal mass migrations, congregating in massive breeding mounds in shallow coastal waters during the summer. Highly prized as a culinary delicacy across southern Europe, it supports valuable artisanal and commercial pot fisheries.
Biology and Physical Characteristics
Maja squinado possesses a broadly heart-shaped or sub-pyriform carapace that is densely covered in sharp tubercles, spines, and hooked setae. The front of the carapace features a prominent bifid rostrum composed of two stout diverging spines. It has ten pereiopods (limbs), including eight remarkably long, slender walking legs that confer its spider-like appearance, and a pair of anterior chelipeds (claws) that are relatively slender compared to those of cancer crabs. Coloration varies from yellowish-orange to dark reddish-brown, often overgrown with living algae, sponges, and bryozoans that the crab deliberately attaches to its shell for camouflage.
Behavior and Ecology
Young spider crabs exhibit fascinating ‘decorator’ behavior, using specialized hooked hairs on their carapace to attach fragments of living seaweeds, hydroids, and sponges, rendering them virtually indistinguishable from the surrounding seabed. As they reach sexual maturity, they undergo a terminal molt, ceasing growth and shedding their decorator habits. In late spring and summer, adult spider crabs migrate into shallow inshore waters, forming colossal heaps or mounds containing hundreds of tightly packed individuals. This aggregation behavior provides communal protection from predators like seals and rays during the vulnerable molting and mating period.
Conservation and Human Impact
The European Spider Crab has not been globally evaluated by the IUCN, but regional fisheries assessments categorize it as stable. It is the target of significant commercial trap and tangle net fisheries in France, Spain, Portugal, and the UK. To prevent overexploitation, European fisheries regulations enforce Minimum Landing Sizes (MLS) and prohibit the landing of berried (egg-carrying) females. Management quotas and seasonal closures during peak spawning help ensure sustainable harvest levels.
Interesting Factoid
During the summer breeding season, European Spider Crabs form living defensive pyramids or ‘heaps’ up to two meters high in shallow water, packing themselves tightly together so that their sharp spiny shells protect soft, newly molted crabs inside the mound from predators.