The European spider crab undergoes a dramatic transformation from microscopic larva to seafloor giant.

Nature · Published 3 October 2026 Swipe more like this →

In short: The spiny spider crab, Maja squinado, begins life as a tiny, planktonic creature weighing just 0.12 milligrams. Over years of molting and migration, it evolves into a formidable inhabitant of the Mediterranean and Atlantic, eventually reaching a size that makes it a significant, yet increasingly endangered, target for commercial fisheries.

The life cycle of Maja squinado is a complex journey of growth and metamorphosis. Hatching at a length of just over 1 millimeter, the larvae spend their earliest days in a planktonic state before transitioning to a benthic, or seafloor-dwelling, existence. This transition is perilous; laboratory observations suggest that only about 10.5% of hatched zoea successfully reach the first juvenile stage. From there, the crabs embark on a two-year period of steady growth, molting frequently while residing in shallow coastal waters, such as kelp forests in winter or rocky reefs during the summer months.

Sexual maturity is reached only after a series of critical molts, specifically the prepubertal and pubertal stages. These events typically occur between April and October, though the timing can be flexible; some large individuals may skip a molt or, conversely, undergo three in a single cycle. The growth rate slows as the crab ages, with the carapace length increasing by approximately 36% during the prepubertal molt, compared to a 27% increase during the pubertal phase. Once mature, these crabs are known for their migratory behavior, with some individuals traveling over 160 kilometers in eight months.

The species is highly valued in commercial fishing, with annual catches exceeding 5,000 tonnes. France leads production, accounting for over 70% of the total, followed by the United Kingdom and the Channel Islands. Despite regulations like the European Union's 120-millimeter minimum landing size and regional bans on harvesting egg-bearing females, the population faces significant pressure. Environmental degradation and management challenges have left the species endangered, complicating efforts to sustain this vital marine resource while balancing the needs of local ecosystems and the fishing industry.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• The European green crab is a global invader currently being turned into dinner.
• The brown crab is a master of the sea, wearing a pie crust shell.
• Why some crabs have abandoned the ocean to conquer the land for good
• True crabs hid their tails and conquered the seafloor
• Mangrove crabs are the master engineers keeping tropical coastlines alive and nutrient-rich
• The giant freshwater prawn uses a complex social hierarchy to dictate its own growth
• Meet the gladiators: ancient, wingless insects hidden in plain sight until 2001.
• Why the world’s most destructive moth was recently renamed to the spongy moth
• Why the world's largest aquatic insect spends years underwater before its fleeting adult life
• Why the seed bug family is far smaller than it used to be
• Was the giant prehistoric insect Meganeura actually a victim of its own massive size?
• The Luna moth lives for only one week and never eats a single meal.

More in Arthropods · More in Nature · Latest · A–Z · All topics