What Divers Should Know About Hermit Crab

The most distinctive feature of a hermit crab is its soft, spirally curved abdomen, carefully tucked away inside a scavenged gastropod shell. This essential mobile shelter protects their fragile, non-calcified exoskeleton, a unique adaptation among decapod crustaceans. Without these borrowed homes, their vulnerable bodies would be defenseless against predators, highlighting a remarkable evolutionary solution for survival.

This strong reliance on salvaged shells has led to incredible diversity within the Paguroidea superfamily, with over 800 known species. You can encounter these fascinating creatures in almost all marine environments. While many species measure only a few millimeters, others, like the Indos Crab (Coenobita brevimanus), can grow to the size of a coconut and live an impressive 12 to 70 years.

Mostly nocturnal, hermit crabs are omnivorous scavengers, constantly on the move in search of food and, often, a new, larger shell to call home as they grow. When approached, their entire body can quickly retract into their protective shell. Their constant search for suitable shelter and varied forms make them a captivating subject during any dive.