Hermit crabs are found both on land and in water. Whether they are land or marine crabs, they are crustaceans that live in a shell discarded by another animal. This article talks about the peculiarities of “terrestrial” or “arboreal” hermit crabs, not oceanic varieties.
They really start life as fish and turn into terrestrial life. These little crabs start out in the ocean, much like sea hermit crabs. While in the water as babies, hermit crabs start out as larvae called zoeae and develop into aquatic crabs, swimming and breathing underwater through gills. As adults, they can no longer breathe underwater, but still breathe through gills that must be kept moist to avoid suffocation. Adult hermit crabs have lost the ability to swim.
The shape of its tail is determined by its first shell. The back of a hermit crab curves to fit and cling to the shell in which it lives. The shape of their first shell is very important and will influence their shell selection for the rest of their lives.
They “go number one” under your eyes. Hermit crabs excrete urine through glands at the base of their antennae. Which means they “pee” through the face.
Your name is inappropriate. Although these animals are commonly called “hermit crabs”, they are not actually true crabs because they lack hard armor on the abdomen, 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 that is not where the stocks in pet stores come from. All available pet livestock have been harvested from beaches around the world where these animals are native. Most of the hermit crabs as pets in the US come from the western Atlantic shores.
They do not have vocal cords, but they still “speak”. These cute little crustaceans make squeaking sounds when rubbing their legs. This is called “stridular” and it works in a similar way to the noise you get when you rub both hands together. They can be very expressive.
They move. To grow, this crustacean has to go through the process of burying itself, shedding its old exoskeleton, eating it, and re-emerging. This is called shedding and it can all take weeks. Without a safe place to bury itself for weeks about once or twice a year, a hermit crab will die.
Generally, only six of its ten legs are visible. Although hermit crabs have ten legs like a spider, they keep the four hind legs inside their shells to anchor them and keep the inside of the shell clean.
The legs can be “pulled” without killing the crab. If a crab is stressed or scared, it may “let go” of a leg to distract a threat and hopefully escape. Sometimes they also do this when they are sick. They will grow a new leg in the oven in the next few molts.
Hermits poop. Their owners sometimes wonder if they do it, because crab poop is small and mixes with bedding materials. These guys defecate inside their shell and then pull it out or scoop it out the side of their shell.
Hermies have long been adored as short-term pets that are easy to care for. They can actually live up to 30 years or so in captivity if cared for properly. Pet stores routinely provide poor care for hermit crabs and pass on poor pet care information to owners, resulting in a shorter lifespan. As a highly misunderstood pet, they have a strong following of online devotees who distribute good care information.