Hermit Crab

A 10-gallon tank is an absolute floor, but 20 gallons or more is far more appropriate — and necessary for a group, since hermit crabs are social and should be kept with at least 2 to 3 others, not alone. This is one of the most under-communicated requirements in the pet trade. Humidity must stay at 70 to 80%, measured with a hygrometer rather than guessed, since hermit crabs breathe through modified gills that need consistently moist air; a secure lid, substrate misting, and a mostly covered tank all help maintain this. Deep substrate — a sand and coconut fiber mix at least three times the crab's body length — is essential, since crabs burrow completely underground to molt, sometimes for weeks at a time. Provide both a freshwater pool and a marine saltwater pool, each deep enough to submerge in but with an easy exit ramp to prevent drowning, using only dechlorinated water. Keep temperatures at 75 to 85 degrees F, and always have 2 to 3 spare empty shells per crab, slightly larger than their current one, available so they can upgrade as they grow.

Hermit crabs are omnivorous scavengers. A commercial hermit crab food can form a base, but a genuinely varied diet of fresh fruit, vegetables, unseasoned meat, and calcium sources like cuttlebone or crushed eggshell makes a real difference in health and molt success. Avoid pre-packaged shells or substrate treated with paint, dye, or chemicals, and never offer any food that has been near soap, pesticides, or copper-based products — all are toxic to hermit crabs. Feed daily in a shallow dish and remove uneaten fresh food within a day to prevent mold in the humid enclosure.

Hermit crabs are highly social, and keeping a single crab alone is a well-documented contributor to poor health and a shortened lifespan — groups of several allow the natural social interaction this species needs. Climbing branches, cork bark, and fishnet or plastic mesh support their active, exploratory nature. Always keep several appropriately sized spare shells available so crabs can choose and switch between them, which is itself a form of enrichment as much as a physical necessity. A crab that suddenly burrows and disappears for weeks is very likely beginning to molt, not sick or dead — resist the urge to dig them up to check.

Incorrect humidity is the single leading cause of death in pet hermit crabs — too dry an enclosure causes their gills to dry out and the crab to slowly suffocate. Molting is a vulnerable, weeks-long underground process, and a buried, motionless crab should never be dug up or disturbed. Shell shortage stress occurs when no appropriately sized replacement shells are available, forcing crabs to fight over shells or remain in an outgrown one that restricts their growth. Isolation stress from being kept alone is a well-documented contributor to premature death. Avoid painted, glued, or otherwise 'decorative' shells sometimes sold in stores, which can be toxic or physically restrictive.