Hermit Crab
Hermit crabs are known for their habit of claiming shells of other animals as their “homes” in order to protect their vulnerable bodies.
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Anomura
Superfamily: Paguroidea
Species: Nearly 800 species in 8 families
Common Names: Hermit Crab
Hermit crabs often compete with each other for shells, in places where acceptable shells are scarce. In areas where there aren’t enough shells, some crabs will resort to other items, including man-made items like tin cans. This is not healthy for the crabs, and often results in them dying.
Most hermit crabs prefer an environment in or near water. Some live completely submerged in water, while others live in or around tidepools. Still others are completely land based.
Hermit crabs will sometimes associate with other animals, both within and outside of their shells. Nereid worms often occupy hermit crab shells alongside the crab, helping to keep it clean. Sea anemones may also attach to the outside of the shells.
Hermit crab females are usually ready to mate just before moulting (the process of shedding their shells as they grow). If a male comes across a female preparing to moult, he may grab on to her for some time to ensure he is in nearby when she is ready to mate. The hermit crabs must both leave their shells in order to mate.
Hermit crabs are invertebrates with tough outer exoskeletons on the front part of their body. However, unlike many other crustaceans, the rear part of their body (called the abdomen) is soft and uncovered. These creatures must seek out protection by adopting another structure as their “home”, usually a discarded shell of a sea snail.
Hermit crabs vary in size, with some species only being a few millimeters, while others can grow to a body size of several inches. The largest hermit crab, the coconut crab, is shell-less and can have a body length of up to almost a foot and a half long.
Hermit crabs are able to retract their bodies completely into their shell-home, and usually only the head, legs and claws are visible, with the rest occupying the shell. When a hermit crab outgrows its shell, it must search for a new, larger one.
Hermit crabs’ unique behavior of living in the shells of sea snails dates back to the Late Cretaceous Period, near the end of the time of the dinosaurs, around 70 million years ago. However, even before that they were using the shells of prehistoric ammonites. The earliest examples of hermit crabs date back to the beginning of the Jurassic Period.
Hermit crabs are often kept as pets. Some underwater species are kept in tanks with other saltwater reef fish. Several other terrestrial (land-based) crabs are also kept as pets. They are often seen as “starter” pets that are only believed to live for a short time, but some species, if cared for correctly, may live well over 20 years.