What does a hermit crab need?

Two land hermit crabs need at least 76 liters (20.1 gallons), from The Unusual Pet Vets’ 38 liters per crab for the Australian species, and Aliso Beach Animal Clinic, a California vet clinic, gives 20 gallons or more for two adult Caribbean hermit crabs. Aliso Beach adds deep sand, warm humid air, fresh and salt water and spare shells.

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Which hermit crabs this covers

Aliso Beach Animal Clinic’s guide is mainly about the Caribbean hermit crab, or purple pincher (Coenobita clypeatus), the land hermit crab most often kept as a pet. It says needs vary by species. Zubair Khalid, a vet, writes about land hermit crabs on his personal site. The Unusual Pet Vets, a vet clinic in Australia, covers only the Australian land hermit crab (Coenobita variabilis).

Tank

For two crabs, The Unusual Pet Vets’ figure comes to 76 liters (20.1 gallons), just over Aliso Beach’s 20 gallons (75.7 liters). Aliso Beach says some veterinary references give 10 gallons as the minimum for one or two crabs, but calls 20 gallons or more a more practical start, with room for deep substrate, water pools, a temperature gradient, spare shells, climbing and separate hides. The Unusual Pet Vets adds that ventilation should be low, so the humidity doesn’t drop.

Company

Aliso Beach Animal Clinic says land hermit crabs are social and are generally kept in compatible pairs or groups, when there’s enough space and enough shells, food and water to go round. The Unusual Pet Vets says the Australian species thrives in groups.

Temperature and humidity

Aliso Beach Animal Clinic asks for a gradient rather than one temperature: a warm area around 80 °F (27 °C) and a cooler area the crab can move to. Any heater goes on a thermostat, placed so the crabs can’t touch a hot surface, and it says to avoid hot rocks. Zubair Khalid gives 24–29 °C (75–85 °F) in the middle of the tank.

For the Australian species, The Unusual Pet Vets fixes a reptile heat mat or heat cord to the outside of the back wall, above the substrate, on a thermostat, for 26–32 °C.

Aliso Beach aims for about 70–90% humidity, read on a digital hygrometer rather than judged by eye. Zubair Khalid gives 70–80%, and The Unusual Pet Vets 70–85% for the Australian species.

Substrate

Hermit crabs bury themselves to moult. Aliso Beach Animal Clinic suggests washed sand mixed with coconut fiber, about 5 to 1, at least three times the height of the largest crab deep and deeper for big crabs. Zubair Khalid gives 15 to 20 cm (6 to 8 in), or two to three times the height of the largest crab’s shell. For the Australian species, The Unusual Pet Vets uses children’s play sand and coir peat, 8 to 1, at least 15 cm deep.

Water

Aliso Beach Animal Clinic says land hermit crabs need two water dishes at all times, neither of them metal: one of fresh water treated for chlorine and chloramine, and one of salt water made with marine aquarium salt as its maker directs. Don’t use table salt or Epsom salt.

Shells

Keep several natural, unpainted shells for every crab, some near the size of its current shell and some a little bigger, Aliso Beach says. The Unusual Pet Vets warns that the paint on painted shells can be toxic.

Food

Aliso Beach Animal Clinic calls hermit crabs omnivorous scavengers that need variety: a commercial hermit crab diet as part of it, with foods such as leafy vegetables, carrots, peppers, a little fruit, unsalted nuts, seaweed and unseasoned protein like dried shrimp. Feed in the evening, when they’re active, take out spoiled leftovers the next day, and avoid salty, seasoned, processed or moldy food.

Moulting and handling

Never dig up a buried crab to check on it, Aliso Beach and Zubair Khalid both say: it may be moulting, which takes days to weeks or longer (Aliso Beach); Zubair Khalid says weeks to months. If you have to pick one up, support it by its shell over a soft surface, never pull it out of its shell, and don’t handle a crab that is moulting or just has. The Unusual Pet Vets adds washing your hands before and after.

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