Shell Evacuation in Hermit Crabs

Causes, Treatment, and Prevention

hermit crab without shell
Luis Diaz Devesa / Getty Images

Shell evacuation isn't necessarily an indication that something is wrong with your hermit crab. These popular pet crabs periodically abandon their shells as they grow and move into bigger ones. However, stressful situations may cause untimely shell evacuation, and a homeless crab is an unhappy crab. Without a shell, a hermit crab is more vulnerable to the outside environment; its exoskeleton will get too dry, and the crab will become lethargic. Crab owners can help their pets find new homes before their health declines.

What Is Shell Evacuation?

Shell evacuation happens when a growing crab needs to "trade up" both its housing and its exoskeleton to accommodate its larger body size. This is a normal process called molting and is not a cause for concern. But, not all crabs that abandon their shells are molting. Stress, an inhospitable environment, a poor-fitting shell (too large, too small, too heavy), fungus, or uninvited company can all cause a hermit crab to leave its shell. When this happens, the homeless crab suddenly becomes exposed to its surroundings, which is bad for its health.

Symptoms of Shell Evacuation in Hermit Crabs

If your crab is molting, you may notice that it looks pale, gorges on food, tries to climb the glass walls of its habitat, or stays near its water source. These are pre-molt behaviors. If you notice any of these signs, and your crab's environment is clean and uncrowded, watch to see if your crab sheds its shell and exoskeleton within a few days.

If your crab isn't molting, but it leaves its shell, then there may be a problem due to an unsuitable environment or stress from overcrowding, In this case, you may notice symptoms of distress, as follows:


  • Shell evacuation
  • Desiccation (dryness of the exoskeleton)
  • Lethargy
  • Fungus inside the abandoned shell
  • Sand or other foreign material within the shell

The symptoms of stress-induced shell evacuation differ from those of molting in that they indicate ailing health or a problem that can be identified (such as fungus growing inside the crab's abandoned shell). These symptoms may not be immediately recognizable upon evacuation, so watch your crab closely for a couple of days to determine the cause of evacuation and the need for intervention.

Causes of Shell Evacuation

Stress-induced shell evacuation can be caused by several factors, including:

  • Stress from transportation or handling
  • Habitat humidity levels that are too low or too high
  • Habitat temperature that is too high
  • Fighting with other crabs
  • Fungal growth inside the shell (crabs may stash bits of food that become moldy, or high humidity can encourage fungi)
  • Bacterial infection
  • Foreign material (like sand) inside the shell
  • Mites inside shell

Diagnosing Shell Evacuation in Hermit Crabs

There is no official diagnostic process or testing to determine the cause of shell evacuation, but observing your crab and evaluating its molting stage and habitat conditions will help you figure out what's going on with your homeless hermit crab.


When a hermit crab is out of its shell, it's stressed and vulnerable. Your crab needs protection from the other crabs in the habitat, as well as a little coaxing so that it will return to its shell.

Protect your hermit crab by moving it to an isolation tank or sectioning off a portion of its habitat. The isolation area should have food, water, and about six inches of substrate so that your crab can bury itself and complete its molt if needed. The molting cycle can take up to one month.

An empty shell selection, including several different sizes, should always be available in the habitat to promote easy transfer to a new hermit home.

Fungal or bacterial infections are usually self-limiting and go away after a molt.

Leave your crab alone in a dark habitat for a few days. The peace and quiet will, eventually, help it feel secure enough to try on another shell.

Illustration of ways to encourage your hermit crab back into its shell
The Spruce / Kelly Leigh Miller

Prognosis for Crabs with Shell Evacuation

Evacuated hermit crabs will fare just fine if given the proper environment, time, and shell availability to choose a new home. But, if a stressed crab does not receive attentive care to improve its environment, then its health may fail, and the crab could die.

How to Prevent Shell Evacuation

You can prevent unwarranted shell evacuation by carefully caring for your crab and its habitat. To do so, make sure your hermit crab enclosure has ideal humidity levels (between 70 and 80 percent). Humidity is critical to hermit crab health, as moisture helps them breathe through their modified gills. A hygrometer will help you assure your levels are on target. Also, mist your crab a few times a day with warm distilled water to moisten the gills on the sides of its body.

The hermit crab habitat also requires a strictly regulated temperature range between 72 and 80 degrees Fahrenheit. Maintaining this temperature will allow the substrate in your tank to hold a similar temperature gradient, keeping your crabs warm when they burrow.

To prevent fungal and bacterial infections, make sure your crab's environment has ample airflow, always feed it fresh food, and remove any uneaten food before it grows mold. Clean and maintain both the substrate and the water regularly to prevent the growth of mold or algae.

Some crabs are quite particular about the shape of the opening and the style of the shell, so try to provide slightly larger shells with the same style as that of their prior home. Before placing the new shells in the habitat, wash them and brush off any debris, sterilize them for 15 to 20 minutes in boiling water, dry them, and then make sure there are no foreign objects lodged inside. After the shells are clean, mist them with a mixture of de-chlorinated sea-salted water, and place them in the tank with your isolated crab.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
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  1. My Hermit Crab Has Left its Shell. What do I do? Land Hermit Crab Owners Society.