Hermit crabs are found both on land and in water. Whether they are land or sea crabs, they are crustaceans that live in a shell discarded by another animal. This article is talking about the peculiarities of “land” or “tree” hermit crabs, not the ocean varieties.
They truly start life like fish and grow into land life. These little crabs start out in the ocean, much like sea hermit crabs. While they’re in the water as babies, hermit crabs start out as larvae called zoeae and grow into aquatic crabs, they swim and breathe underwater through gills. As adults, they can no longer breathe underwater, but they still breathe through gills that must be kept moist to prevent suffocation. Grown up hermit crabs have lost their ability to swim.
Their tail shape is set by their first shell. A hermit crab’s rear end curves to fit into and hold onto the shell they live in. The shape of their first shell is very important, and will influence shell selection for the rest of their lives.
They “go number one” below their eyes. Hermit crabs excrete urine through glands at the base of their antennae. Which means that they “pee” through their faces.
Their name is a misnomer. Although these animals are commonly called “hermit crabs” they are actually not true crabs because they lack a hard abdomen armor, and they are not hermits, because they live in large groups of about a hundred crabs in the wild.
Hermit crabs have been bred in captivity, but this is not where pet store stock comes from. All pet stock available has been harvested off beaches throughout the world where these animals are native. Most pet hermit crabs in the US come from the West Atlantic coasts.
They have no vocal cords, but they still “talk”. These cute little crustaceans make sounds sort of like chirps by rubbing legs together. This is called “stridulating” and works similar to the noise you get when you rub your two hands together. They can be very expressive.
They molt. To grow, this crustacean has to go through process of burying themselves, shedding their old exoskeleton, eating it, and re-emerging. This is called molting, and the whole thing can take weeks. Without somewhere safe to bury themselves for weeks approximately once or twice a year, a hermit crab will die.
Only six of their ten legs are generally visible. Although hermit crabs have ten legs like a spider, they keep the back four inside their shells to anchor them in and keep the inside of the shell clean.
Legs can be “thrown off” without killing the crab. If a crab is stressed or scared, they can “drop” a leg to distract a threat so that they can hopefully get away. They sometimes do this when they are sickly, too. They will grow a new leg back oven the next few molts.
Hermits do poop. Their owners sometimes wonder if they do, because crab poop is small and blends in with bedding materials. These guys either defecate inside their shell and then scoop it out or out the side of their shell.
“Hermies” have long been adored as short-term pets that are easy to care for. Actually, they can live up to 30 years or so in captivity when cared for correctly. Pet stores routinely give poor pet care to hermit crabs, and pass poor pet care information to owners, resulting in short lifespans. As a very misunderstood pet, they have a strong grass-roots following of devotees on-line distributing good care information.