Frequently Asked Questions
The most-asked questions about hermit crabs.
What is a hermit crab?
A hermit crab is any member of the superfamily Paguroidea, a group of decapod crustaceans whose soft, uncalcified abdomen must be tucked into a borrowed gastropod shell for protection. More than 1,000 species occupy marine, brackish, and even fully terrestrial habitats worldwide.
Why don't hermit crabs grow their own shell?
Their abdomens remain soft and spiraled rather than being enclosed in a hard carapace, so an internal shell is anatomically impossible. Instead they scavenge empty snail or whelk shells and swap to a larger one each time they molt and grow.
How does a hermit crab change shells?
When it outgrows its current shell, the crab searches for a suitably sized replacement, often triggering a chain of simultaneous trades among several individuals. The swap can take minutes to hours, and the crab is extremely vulnerable the whole time.
Where do hermit crabs live?
The vast majority inhabit shallow coastal waters, rocky reefs, and sandy shores in tropical and subtropical oceans. A smaller number, including the coconut crab and various land hermit crabs, have adapted to life entirely on land near coastlines.
How big can hermit crabs get?
Sizes range from a few millimeters in dwarf species to the coconut crab (Birgus latro), whose leg span can exceed one meter and whose mass approaches 4 kg. Most commonly encountered marine species stay between 2 and 10 cm.
What do hermit crabs eat?
They are opportunistic omnivores, grazing on algae, detritus, small invertebrates, and decaying organic matter. Terrestrial species will also take fruit, fungi, and even human food scraps when available.
Can hermit crabs be kept as pets?
Several land-dwelling species, especially Coenobita, are popular in the hobby, but they need a humid, well-ventilated enclosure, both fresh and saltwater dishes, calcium sources, and multiple shells of varying sizes. Marine species are far more demanding and rarely suited to a home aquarium.
How long do hermit crabs live?
Lifespan varies widely by species and environment; small marine species typically live 2 to 5 years, while land hermit crabs in the wild can reach 10 to 20 years. The coconut crab is the longest-lived crustacean, with documented individuals surpassing 60 years.
Are hermit crabs aggressive toward other animals?
They are not true predators, but they compete fiercely with conspecifics over shells, food, and territory, sometimes inflicting injuries. They can also be nipped by larger tankmates, so housing compatibility is important in any enclosure.
How are hermit crabs different from regular crabs?
True crabs (family Brachyuridae) have a hard, symmetrical carapace covering the entire body, whereas hermit crabs possess a soft, spiraled abdomen that must be sheltered externally. This single anatomical difference drives nearly every other behavioral and ecological distinction between the two groups.