Hermit Crab Gangstas

The University of California Berkley has released an interesting paper on the “gang” habits of hermit crabs. In essence, these small beach creatures bare no relation to their name at all, at least as far as their behavior goes.

Hermit crabs, it turns out, are very sociable and they run in packs. They actually gang up on other crabs and “evict” them from their shells.

Once their victim has been kicked out of his or her shell, by being violently yanked and pulled by those in the gang, the gang members who kicked the now homeless crab out will get in line, largest to smallest, and see which crab fits perfectly into the new shell.

The next crab in line gets that crab’s shell, so on and so forth, so that by the time the crab at the end of the line is fitted in its new shell, the smallest shell is left, and it’s the larger crab who is now homeless, making him a sitting target for predators, and putting him in greater danger of being harmed or even killed by the heat of the sun.

If left exposed to the sun and predators for too long after having lost their shells in a gang fight, it’s not long before a hermit crab will die.

Most of the 800 or so species of hermit crab live in the ocean, where empty snail shells are common because of the prevalence of predators like shell-crushing crabs with wrench-like pincers, snail-eating puffer fish and stomatopods, which have the fastest and most destructive punch of any predator.

On land, however, the only shells available come from marine snails tossed ashore by waves. Their rarity and the fact that few land predators can break open these shells to get at the hermit crab may have led the crabs to remodel the shells to make them lighter and more spacious

Hermit crabs are decapod crustaceans of the superfamily Paguroidea.Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell carried around by the hermit crab.

Most species are aquatic and live in varying depths of salt water, from shallow reefs and shorelines to deep sea bottoms. Tropical areas host some terrestrial species, though even those have aquatic larvae and therefore need access to water for reproduction. Most hermit crabs are nocturnal.

A few species do not use a "mobile home" and inhabit immobile structures left by polychaete worms, vermetid gastropods, corals, and sponges.

Hermit crabs are more closely related to squat lobsters and porcelain crabs than they are to true crabs (Brachyura). However, the relationship of king crabs to the rest of Paguroidea is a highly contentious topic. Many studies based on physical characteristics, genetic information, and combined data support the longstanding hypothesis that the king crabs in the family Lithodidae are derived hermit crabs and should be classified as a family within Paguroidea.

In general, and despite their common name, hermit crabs are social animals that do best in groups. In the wild they can be found in colonies of a hundred or more. Therefore, many sellers encourage the purchase of more than one crab.