Unlike most other crustaceans, adult hermit crabs live their lives on land, rather than in the ocean. This fact has led to a variety of hermit crab adaptations making the crab ideally suited to its open-air environment. First, their gills have developed over time so that they can breathe in moist air. In captivity, hermit crab owners must provide their crabs with a humid environment so that they are able to breathe. Still, the hermit crab has not completely adapted to living away from the shore. At humidity levels under 70 percent, such as that found inside the typical home, the gills dry up and are unable to take in oxygen.
Although baby hermit crabs are born in the water, by the time they become adults they are completely adapted to life on land. In fact, they cannot survive if submerged in water for long periods of time, despite having been born in the ocean. As the babies grow, they lose the ability to breathe underwater. Their modified gills are no longer able to take in oxygen from liquid water, even though they need moisture in the air. As a hermit crab owner, it’s important to consider this adaptation when planning your pet hermit crab’s habitat. In water dishes that are too deep, your hermit crab may fall in and even drown. However, in environments that are too dry the crab becomes unable to breathe.
In contrast to other crustaceans, such as lobsters and crabs, the hermit crab’s shell is not his own. In fact, the crab itself has a relatively soft body and exoskeleton. If left unprotected, this small creature would easily fall prey to a variety of predators, from larger crabs to seagulls. As a result, the hermit crab has learned to quickly inhabit the discarded shell of another animal. In the wild, baby hermit crabs seek out the shells of sea snails, although they’ve also been found wearing everything from a plastic bottle cap to an airline liquor bottle. In order to carry this shell on his back, the hermit crab has evolved to have very strong back legs, which clasp onto the inside of the shell so that it will stay on as the crab crawls. This hermit crab adaptation has enabled the crab to protect its body from predators who would otherwise be able to eat it.
Another one of the hermit crab adaptations to life on land comes in the form of a nocturnal lifestyle. Because most of the crab’s natural predators are most active during the day, crabs tend to hide during these hours. At night, they are at their most active, when the chance of being spotted by a predator is lower. Even in captivity, you will notice increased activity from your hermit crab at night. During the day, he will hide in a clay flower pot, a coconut shell, driftwood, or anything else you put in his cage.
Hermit crabs are fascinating creatures to watch, especially if you consider how well adapted they are to life on land. The key to caring for them correctly is understanding their natural environment and how they live.