Hermit crab uses 'walking coral' as home

Hermit crabs are well known for making their homes out of empty shells. They will go from shell to shell throughout their lifetime trying to find the perfect fit and to gain better protection. However, it has recently been discovered that shells are no longer the only objects hermit crabs are using for protection. A species of hermit crab located in the Amami Islands, which is part of a chain that stretches southwards from Japan towards Taiwan, has been found to be using solitary corals for their shelter. This species of crab is named Diogenes heteropsammicola, after the species of coral that they inhabit.

Hermit crab (Diogenes heteropsammicola)

This relationship has proved to be mutually beneficial for both the hermit crab and the coral. By using coral as its protective armor the hermit crab no longer has to continue to search and search for new and better shells as it continues to grow. The space in the coral in which the hermit crab sits grows with the crab, so it does not need to search and compete among its species for new homes. In addition, the coral is able to sting, which helps to further protect the crab from predators such as starfish, larger crabs, and octopi.

A type of coral the hermit crab will use (Heteropsammia cochlea)

This relationship is also able to be favorable for the coral as this species of coral is a solitary coral instead of a reef-building kind. Solitary corals are often found on shallow sandy seabeds. With this type of habitat, the solitary coral runs the risk of being buried by sediment and overturned by strong currents. To combat this, corals will develop a partnership with other animals to assist them out of the sand and do the ‘walking’ for them. This is usually seen with marine worms, but is now prevalent in this hermit crabs species as well.

Coral skeleton after being used by hermit crab

Though more research needs to be done, it is thought this relationship with hermit crabs developed similarly to how the marine worms use the coral for protection. In the case of the marine worm, a young coral will settle on a small shell that has already been colonized by the marine worm. The coral then grows over and beyond the shell, providing a cavity for the marine worm, which is continuing to grow as well. These hermit crabs likely acquire coral shelter and develop this symbiotic relationship in a similar manner such as this one.




Mynott, S. (2017). Newly discovered hermit crab species lives in 'walking corals.' The Conversation, 12 March 2018.