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Hermit Crab

Invertebrates

The shell-swapping beach scavenger that is nobody's starter pet!

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🤓 Did you know? Hermit crabs don't grow their own shells - they spend their entire lives searching for, trying on, and trading empty snail shells as they grow, and will even form an orderly 'vacancy chain,' lining up by size to swap shells in turn when a larger one becomes available. In the wild, land hermit crabs can live 20 to 30+ years, though most pet hermit crabs sold in beach-town gift shops die within their first year from incorrect humidity and being kept alone.

🗓️ The first week

The numbers a new owner needs in the first week, each from the article it links to. Rows with no link come from the encyclopedia.

Tank: A glass terrarium, roughly 10 gallons for 2 to 3 small crabs, more for bigger crabs or groups, with a glass or acrylic lid that seals in humidity. Cover part of a screen lid with plastic wrap.Setup guide →
Group size: At least two. They are social.Setup guide →
Temperature: 75 to 85°F, the warm side around 80°F, from a side- or back-mounted heat mat. Never under the tank: heat rising through deep substrate can kill a buried, molting crab.Setup guide →
Humidity: 75 to 85%, on a hygrometer, held with moist substrate, a sealed lid, and a moss pit.Setup guide →
Substrate: Play sand and coconut fiber at about 5:1, packed to sandcastle consistency, at least 6 inches deep or 3 times the height of the largest crab. They burrow to molt.Setup guide →
Water: Two soakable dishes, one dechlorinated fresh, one marine saltwater from an aquarium salt mix, never table salt. Deep enough to submerge, with an easy way out, since crabs drown.Setup guide →
Shells: 3 to 5 or more natural, unpainted shells per crab across a range of sizes. Painted shells are toxic.Setup guide →
Diet: Varied: cuttlebone for calcium, fresh fruit and vegetables, dried shrimp or insects for protein, leaf litter. Fed in the evening, leftovers out in the morning. No UVB requirement, a 12-hour light cycle.Setup guide →
Handling: On a flat open palm, never a closed hand. Lift by the back of the shell, not the legs, and keep it brief.Handling guide →
Buried and out of sight: A new arrival digs down for days, sometimes over a week. A molting crab stays buried for weeks to around three months and is never dug up, however long it has been.Handling guide →
The first molt: Every pet hermit crab is wild-caught, and the adjustment period is where most deaths happen. Isolate new crabs, change humidity and temperature gradually, and count a crab past the risk only after its first molt in your care.Health guide →
Food to avoid: Copper sulfate, toxic to invertebrates, and ethoxyquin, a preservative that hides in fish meal without appearing on the label.Feeding guide →
A lost limb: Regrows over successive molts, first as a small bud.Health guide →
Budget: $3 to $40 per crab, roughly $130 to $450 for a complete setup, then $10 to $30 a month.Cost guide →
Lifespan: 10 to 20 years or more when kept well.Cost guide →
Adult size: Up to 4 inches (10 cm) across, including legs.
Household pesticides: Every insecticide sold for a home kills arthropods, and ant spray in the kitchen, a plug-in in the hallway, or a dog's flea treatment all reach an enclosure.Pesticide guide →
Power outage: The exception among invertebrates: actively heated and humidified, so the risk is a reptile's. A battery backup for the heat and a sealed lid over damp substrate belong in the outage kit.Emergency plan →

🚨 Emergency card

Check heat, humidity and substrate depth first, then act on these today. No practical vet care exists for this animal.

Lethargy, hiding, refusing food, and rapid loss of several limbs: advanced post-purchase stress
An ashy look, lethargy, and an inability to retract fully into the shell: dehydration and gill suffocation
A molt interrupted, or happening in substrate too shallow or dry, which is frequently fatal
Limb loss from stress, fights, mites, or wrong conditions
Mites and mold, from poor hygiene or inadequate ventilation

Correct the husbandry behind it, and isolate any crab that is aggressive, injured, or showing post-purchase stress while it recovers.

From Common Hermit Crab Health Issues (There's Almost No Vet Care, So Prevention Is Everything) →

📰 Where to go next

How Much Does a Hermit Crab Really Cost?

$3 to $40 for the crab itself, why the setup is the part that actually costs money, and the monthly budget after that.

Hermit Crab Enclosure Setup: Humidity, Deep Substrate, and Extra Shells

Humidity, temperature, substrate depth, the two water dishes, and the shells that go in the tank.

How to Handle a Hermit Crab (Minimally, and On Its Terms)

Why handling stays minimal, the open-palm method, and how long a buried crab can stay down.

Common Hermit Crab Health Issues (There's Almost No Vet Care, So Prevention Is Everything)

Post-purchase stress, dehydration and gill suffocation, bad molts, and what seeking help looks like when there's almost no vet care.

Giant Millipede Feeding: The Floor Is the Diet, Produce Is the Treat, and Calcium Stays In

The substrate as the diet, produce every two to three days and out before it molds, calcium left in, and the molt that looks like a fast.

Hermit Crab Enrichment: Shells Are a Welfare Need, Not Decoration

What the shell research actually found, how many shells a group needs, and the priority order for everything else.

🛒 What to buy

Glass terrarium, roughly 10 gallons for 2 to 3 small crabs and larger for a bigger group

A glass or acrylic lid that seals humidity in

Play sand and coconut fiber for substrate

Side- or back-mounted heat mat

Thermometer and hygrometer

Two soakable water dishes, ceramic or otherwise non-metal

Dechlorinator

Marine aquarium salt mix

Natural unpainted shells in a range of sizes, several per crab

Climbing branches and cork bark

Cuttlebone or another calcium source

Hermit crab food plus fresh fruit, vegetables, and protein

Prices and the reasoning behind each item are in How Much Does a Hermit Crab Really Cost?.

❓ Frequently Asked Questions

What humidity level do hermit crabs need?

75 to 85% relative humidity, checked on a hygrometer. It isn't optional: the modified gills a hermit crab breathes through must stay moist to work, and humidity below that range leads directly to dehydration and gill suffocation.

When should I never handle my hermit crab?

Never handle a crab that's molting, has recently changed shells, or is buried in the substrate. Molting crabs are extremely vulnerable, and disturbing one during this time can be fatal, it's one of the clearest rules in hermit crab care.

What's the leading cause of death in pet hermit crabs?

Post-purchase stress, since every pet hermit crab is wild-caught rather than captive-bred and goes through real shock from capture, shipping, and a new environment. Watch for lethargy, burrowing, refusing food, and rapid loss of multiple limbs, and know that a crab generally isn't past the risk period until it has molted once successfully in your care.

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Hermit Crab

Coenobita clypeatus

Animal facts & overview