Health: What to Do When a Crab Is Out of Its Shell

[HCADirectors]

Guide written by JoeHermits of the Hermit Crab Association.

In certain situations, a hermit crab may leave its shell without acquiring a new one, usually as a result of stress or weakness. When that happens, your priority is getting it to wear a shell—without one, the crab’s abdomen is vulnerable to injury and desiccation.

Before you do anything, make sure your hands are clean and free of soap, perfumes, lotions, or other chemical residues.

Plan A: Isolation

1. Scoop up the streaking hermit crab with a container just large enough to hold both it and a few appropriately sized shells. For smaller crabs you may use a glass or cup, but a plastic or glass food container will work better in most cases.

2. Pick up the crab in your hand and dip it in a cup of lukewarm dechlorinated water to rinse off any substrate. It should be free of all foreign material to reduce irritation and risk of injury.

3. Place about half a centimeter or a quarter of an inch of lukewarm dechlorinated water on the bottom of the container for moisture.

4. Rinse off the crab’s original shell plus one or two others of similar size in dechlorinated water to remove any substrate on or within and place them in the container. If the original shell is lost, damaged, or otherwise unavailable you may use a similar substitute.

5. Place a cloth or towel over the container for darkness and leave in a warm place, preferably in the main tank or an isolation tank. Leave alone for one to two hours.

6. If the crab has selected and moved into a shell, you may return it to the main tank as normal. If it is still naked, move on to Plan B.

Plan B: Manual Re-shelling

1. Scoop up the naked hermit crab in one hand. Select the shell you want the crab to wear and pick it up with your other hand.

2. Let the crab stand on your palm and position the shell behind it so its opening is facing the crab.

3. Lightly tap the crab on the head. It will back up and into the shell.

4. If the hermit crab takes the shell, you may return it to the main tank as normal. If the crab is not re-shelled because it keeps crawling out or otherwise resists in such a way that manual re-shelling is not practical or safe, return to Plan A.

Troubleshooting:

Although we can’t always tell why a hermit crab is streaking there are things that can give us clues. Here are a few things to watch out for if your hermit crab has ditched its shell.

Shell-jacking: Did a tankmate steal the shell? Are there enough shells so everyone can wear what they want? Are spare shells filled with substrate, have holes in the spirals, or otherwise unfit for use?

Temperature: What is the temperature in the tank? Is it above or below your species’ acceptable temperature range?

Humidity: What is the humidity in the tank? Is it below seventy percent humidity?

Water: Have both the fresh and saltwater been treated to remove chlorine, chloramines, and heavy metals? Is the saltwater made from a marine salt formulated to mimic sea salt?

Diet: What has the crab been eating? Does it have a range of macro- and micronutrients available? Has it eaten foods high in pesticides such as conventionally farmed berries or leafy green vegetables? Does any of its food contain ingredients of concern such as copper sulfate or seafood meals containing unlisted ethoxyquin* or butylated hydroxytoluene (BHT)**?

*Ethoxyquin is not used in pet foods manufactured in Australia, Japan, or the United Kingdom.
**BHT is not used in pet foods manufactured in Japan or Australia.

Stuck Shell: Is there a narrow area in the tank where the shell could’ve been caught, either above or below the substrate's surface? Did the crab get stuck and drop its shell to escape?

Post-purchase Syndrome (PPS): Did you obtain the crab within the last year? Has it molted in captivity before?