Sponge Crab

Crustacean

Identification & Biology

• IdentificationA round-bodied crab that carries a living piece of sponge on its back, held in place by modified rear legs. The body underneath is hairy and reddish-brown. The sponge cap is trimmed to fit and grows with the crab, providing both camouflage and chemical defence.
• SizeCarapace width up to 7 cm (not including the sponge). The sponge layer can add several centimetres.
• Social HabitSolitary. Nocturnal. Moves slowly across the reef at night carrying its sponge disguise. When threatened, it relies on the sponge's chemical defences to deter predators.
• HabitatRocky reefs, caves, and mixed substrates. Found wherever suitable sponges grow.
• Depth0 to 100 m. Most common between 5 and 40 m.
• Feeds OnDetritus, small invertebrates, and organic matter found on the reef. A scavenger and omnivore.
• DistributionEastern Atlantic from the British Isles to West Africa, and throughout the Mediterranean Sea. Present in Maltese waters.
• DescriptionDromia personata is one of the most ingenious crabs in the Mediterranean. It carefully selects a piece of living sponge, trims it to fit its back using its claws, and holds it in place with specialised rear legs. The sponge continues to grow, creating a living shield. Many predators avoid sponges due to their toxic chemical compounds, so the crab benefits from chemical warfare without producing the chemicals itself.