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Is My Hermit Crab Healthy?

Forget anything you may have heard about hermit crabs being easy to care for as they’re delicate with very specific care needs.

When keeping hermies in captivity, you must understand the warning signs of ill health.

Happy, healthy hermit crabs will be curious and active, especially after dark. They’ll roam their aquariums, sporting vibrant colors and bright eyes. They’ll be docile and have 10 intact limbs.

If your hermit crabs are sluggish and lethargic, pale, aggressive, or spend prolonged periods hiding, they’re likely unwell.

You should never adopt a sick or diseased hermit crab. While this may seem like an act of mercy, the animal will not survive the shift to captivity.

Common Hermit Crab Health Issues

Unlike mammals, hermit crabs are not susceptible to cancer or other tumorous diseases. Equally, hermit crabs do not fall foul to colds or viral infections, like influenza.

This does not mean that hermit crabs are hardy and immortal, though. Many captive hermit crabs fail to live longer than a few weeks as pets. As they can live as long as 40 years, that is a shocking statistic.

You can keep your hermit crabs happy and healthy, enjoying a long life together. This involves understanding and identifying the risks that daily life poses, though. Captive hermit crabs may not need to worry about predators, but they have plenty of other concerns.


Stress is the most common condition that impacts hermit crabs. These animals are not psychologically equipped to easily adjust to captivity. As breeding is virtually unheard of in such conditions, your pets will almost certainly have started life in the wild.

If you purchased hermit crabs from a seafront gift store, they are likelier to experience stress. The people that run such establishments rarely understand the needs of hermit crabs. They are often forced into uncomfortable, unsuitable living conditions.

When you bring hermit crabs home, they experience a condition known as, “post-purchase syndrome.” This involves hiding under the substrate, potentially for weeks on end. Some hermit crabs survive this, but unfortunately, others do not.

During PPS, all you can do is be patient. The hermit crabs are destressing and adapting to their new living arrangements. If they survive the experience, they will emerge when ready. Never disturb hermit crabs while hiding. This will only magnify their discomfort.

Even after adaptation, hermit crabs are easily stressed in captivity. Keep an eye out for any bullying in the tank. It’s rare, but it does happen. Provide an appropriate habitat, minimize handling and ensure that your hermies are not exposed to excessive light or noise.


Toxicity is a major concern. Many seemingly innocuous materials can kill these animals. The three most common are:

  • Paint flakes, especially from painted or decorated shells
  • Chlorine and copper found in tap water – always provide filtered or distilled water
  • CFCs from aerosol cans used in proximity to a tank, such as deodorant or air freshener

Always be mindful of the threats of toxicity to hermit crabs. Once the damage is done, there is no going back. Outside of stress, this is the most common – and easily avoidable – cause of ill health in these animals.

Difficulty Breathing

Hermit crabs breathe through gills on the side of their body. These gills must remain damp to enable breathing. This means that hermit crabs need constant access to water, and their habitat must be sufficiently humid.

Invest in a hygrometer for your hermit crab tank. This will measure the amount of water vapor in the air and provide a humidity score. Anything below 80% will make it difficult for hermit crabs to breathe.

Hermit crabs cannot hold their breath for long, so they require air as much as any living thing. It’s a simple equation; hermit crabs that lack humidity will slowly suffocate. Unless you take immediate action and increase humidity, this will be fatal.

healthy hermit crab

Overheating or Growing Too Cold

Hermit crabs require particular temperatures to thrive. As tropical animals, hermit crabs can only survive in warm climates. Any temperature that drops below 55 degrees Fahrenheit could be fatal.

Most owners recommend maintaining a hermit crab aquarium’s base temperature of 80 degrees Fahrenheit. If they show any signs of overheating, steadily reduce this temperature until they appear more comfortable.

Mites and Parasites

Mites – and other insects – can be omnipresent in a hermit crab enclosure. As discussed by the Journal of Experimental Marine Biology and Ecology, as many as 140 species of parasites can attach to hermit crabs.

Many breeds of mites are harmless. Even so, these bugs will multiply and spread like wildfire. If left untended, mites can become the dominant species in an aquarium. This will make cleaning and fumigation difficult and time-consuming.

If your hermit crabs have mites, they must be treated. Mites can be hard to spot with the naked eye, but they resemble small white blotches on the legs, body, and eyes. Your pets may bathe more in an attempt to rid themselves of mites and even sever limbs.

Never use an anti-parasite spray in a hermit crab enclosure. These are toxic. Remove any hermit crabs with mites and bathe them in freshwater. Repeat this until the infestation passes. Before returning hermit crabs to their tank, conduct thorough sterilization and cleaning.

Shedding Limbs

Hermit crabs shed limbs when sick or stressed. Equally, hermit crabs may voluntarily sever their limbs. This is common when an injury is sustained, such as falling while climbing the walls of an aquarium.

Hermit crabs do regenerate shed limbs when they molt, so this is not the end of the world. It’s something to keep an eye on if it keeps happening. Happy, healthy hermit crabs will typically retain the use of 10 functional limbs.

Fungal Infection

Fungi can grow and spread in a habitat that ensures excessive humidity. If this fungus starts to grow on the body of your hermit crabs, it must be managed at once. Fungal infections are highly contagious and can be fatal to hermit crabs.

Upon the onset of a fungal outbreak, immediately bathe the infected hermit crab in saltwater. Ensure the fungi have been removed before returning it to share a habitat. Bathe all other hermit crabs as a precaution too.

You will also need to deep clean the aquarium that homes your hermit crabs. Fungal spores can be stubborn. A simple wipe down is not sufficient. Clean the tank thoroughly and replace any substrate and decorations.

Shell Rot

Shell rot is a condition that primarily impacts aquatic hermit crabs. It manifests as dark patches on the exoskeleton, usually black or deep green in shade. These patches will eventually create holes in the exoskeleton, inviting bacterial infection.

Hermit crabs typically develop shell rot through prolonged exposure to dirty water. If you have an appropriate water filter, this should not be a concern. Shell rot can stem from eating contaminated food too, though – including a dead hermit crab.

Shell rot is contagious between hermit crabs, so it should be addressed. Some hermit crabs will take care of the problem themselves by entering a molt. If not, remove any shed limbs that show signs of shell rot and watch the infected crab carefully.

Keeping Hermit Crabs Healthy

Hermit crabs are considered wild animals, not domesticated pets. If you are going to adopt these animals, you need to care for them. That means doing all that you can to prevent ill health from befalling your hermit crabs. The key to protecting the health of hermit crabs are:

  • Providing an appropriate aquarium that closely replicates the natural habitat of your hermit crabs
  • A healthy diet that meets all nutritional needs, in addition to plenty of variety
  • The opportunity to play and exercise, ideally with company – despite their name, hermit crabs are social
Is My Hermit Crab Healthy?

Appropriate Habitat

Before you even consider adopting hermit crabs, you need to ensure they have an appropriate habitat. This means a solid aquarium made from glass or plastic. A solid tank is a must to retain humidity.

Once you have your tank (two tanks – as we’ll explain shortly, you’ll need a second tank to house your crabs while one is being cleaned), you must ensure the habitat meets the following criteria.

  • Temperature of 80 degrees Fahrenheit
  • Humidity level of 80%
  • At least 3 inches of appropriate substrate (ideally 6 inches)
  • Plenty of hiding places
  • Spare shells for when a change is required
  • Toys and obstacles to climb and interact with

Be warned that kitting out the ideal hermit crab habitat can be more expensive than you expected. All the same, this is not a situation where you can cut corners to save a few bucks. Hermit crabs kept in inappropriate conditions will not thrive and rarely survive long.

Cleaning a Habitat

You will need to regularly clean a hermit crab enclosure. This takes two forms – daily spot cleaning and a periodic deep clean. The latter involves temporarily rehoming your hermit crabs while their habitat undergoes a complete renovation.

If you fail to clean a hermit crab aquarium, it will become a bacterial and fungal disaster zone. This increases the risk of sickness and mite infestations. It will also stress out your pets. Hermit crabs are surprisingly meticulous about personal hygiene.

Spot clean the substrate in your aquarium daily. This will remove any uneaten food that may otherwise rot and pick up any waste. Take this opportunity to wipe down the walls with a non-chlorinated water source.

Every three months or so, place your hermit crabs in a different tank overnight and deep clean their aquarium. This involves removing all substrate and decor. This can be replaced or baked in the oven or washed in high heat.

The walls and floor of the aquarium must also be cleaned and left to air dry. Once the habitat has been cleaned and is bone-dry, restore essential components, set the temperature and humidity, and return your hermit crabs to their traditional home.

Healthy Diet

In the wild, hermit crabs scavenge for food and enjoy whatever they can get their claws on. As herbivores, hermit crabs can eat meat and plant matter alike. In captivity, this scavenging is unnecessary. You must still feed a healthy diet, though.

The most important components of a hermit crab diet are protein and calcium. These will provide hermit crabs with a strong, sturdy exoskeleton. Hermit crabs also need carbohydrates for energy. Beta carotene, meanwhile, will provide rich, vibrant color.

There are plenty of foods that hermit crabs can enjoy, whether as a main meal or treats. Keep your hermit crabs interested by varying their diet, though. As explained by Animal Behavior, hermit crabs frequently lose interest in food that they have recently eaten.

Company and Recreation

Hermit crabs take their name from the fact that one crustacean lives in one shell. This does not mean that hermit crabs are loners that prefer to keep their own counsel. The opposite is true. Hermit crabs hate living alone, and only thrive with company.

If you are looking to get hermit crabs, note the plural term. At the very least, bring two hermit crabs into captivity together. Ideally, though, you should not be looking at anything less than four at a time. The more the merrier.

If left alone for too long, hermit crabs grow lonely and withdrawn. This will lead to stress, which in turn causes the shedding of limbs. As per Zeitschrift für Vergleichende Physiologie, too much time alone also makes hermit crabs more aggressive and dominant.

Signs of a Healthy Hermit Crab

Hermit crab owners must always be able to identify a healthy pet – or otherwise. This is especially important if you are choosing hermit crabs to bring home. Hermit crabs that are already sick will not survive the transition to captivity.

Even when your hermit crabs are settled, though, they must still be watched carefully. Keep your eyes – and nose – open for signs of happy, healthy hermit crabs. If your pets do not fit these descriptions, something may be amiss with their well-being.

Physical Appearance

The old-fashioned eye test goes a long way to judge whether your hermit crabs are healthy. Wait for your hermit crabs to wake up and start their day. While they are going about their business, review their physical attributes. Healthy hermit crabs will have:

  • Ten functional limbs – shedding limbs is a sign of stress or sickness
  • Bright, clear eyes that are not milky or glazed
  • A bright, vibrant skin color
  • Moist skin – dry skin leads to scarification around the gills and difficulty breathing
  • No sign of mites, fungi, or other foreign bodies on the body

The one exception to these rules is when hermit crabs are preparing to molt. In such instances, a hermit crab’s skin will fade to gray and their eyes will glaze over. Such hermit crabs will also become more lethargic.

Given time, you will learn the molting schedules of your hermit crabs. Fully-grown adults molt roughly every 18 months. Juvenile and younger hermit crabs molt more frequently though, as they experience several growth spurts in a comparatively short period.


You can also tell a lot about hermit crab health by the smell of their habitat. Healthy hermit crabs should have a comparatively neutral scent. Any funky aromas in a habitat should be restricted to waste.

If you notice a smell of rotten fish, something unfortunate may have befallen one of the hermit crabs in your care. This distinct aroma is usually associated with dead or dying hermit crabs. As per Ecology and Evolution, dead hermit crabs release a pheromone to announce the availability of a shell to conspecifics.

Do not immediately panic if you detect this smell, though. It is unpleasant but does not always announce death. One or more of your hermit crabs may just be molting. In such instances, the shed exoskeleton will rot. Ensure this not the case before taking action.

Appropriate Use of Shell

Your hermit crabs should always carry their shell on their back. Your hermit crab is hanging out of its shell, it is likely overheating. Hermit crabs perform most of their day-to-day tasks within a shell. They do not need to leave the shell to eat or eliminate.

Typically, hermit crabs will only vacate a shell if looking to trade up to a new domicile. All the same, this doesn’t mean that hermit crabs should spend all their time hiding within a shell. This usually means that something is amiss.

Tempt your hermit crabs out their shell with food. If this does not work, handle the crabs and gently blow inside the shell. This should inspire sufficient curiosity to least poke their head out of the shell. Legs should also follow.

If your hermit crabs never leave their shell, they may be stuck. Sometimes this is due to the hermit crabs outgrowing their shell, bit stubbornly refusing to give it up. In other cases, especially with painted shells, the hermit crabs may be ‘glued’ inside.

Either way, hermit crabs should not be forced to live inside a shell they cannot leave. Do not try to yank the hermit crab out of the shell. That will result in pinches and shed limbs. Do encourage such hermit crabs to trade to a different shell, though.

what color is a healthy hermit crab?


Hermit crabs are docile. They usually get along famously with each other, living in colonies too up to 100 members in the wild. Given times, hermit crabs also learn to tolerate – and potentially even enjoy – human company.

Like all animals, hermit crabs will squabble on occasion. Fights over shells are common, as all hermit crabs covet the finest possible domicile. Hermit crabs also like to play-fight for recreation, usually in the form of antennae wrestling.

If stressed or sick, though, hermit crabs can grow uncharacteristically aggressive. This behavior has a similar root cause to all aggressive animals. It stems from fear. Sick or stressed hermit crabs do not want to project an image of weakness.

A healthy hermit crab will usually keep its claws to itself and will not harass or harm tank mates. If any of the hermit crabs in your care show uncharacteristic fits of temper or hostility, ill health is likely to blame.

Activity Levels

Hermit crabs are not lazy animals. They should happily scuttle around in their habitat. As per Marine Biology, wild hermit crabs relocate to a different territory when hunting food or shells. They’ll do the same in captivity. If your hermit crabs are not moving, it’s rarely a good sign.

Ensure your hermit crabs have a reason to move. Food is usually a great motivator. Hermit crabs also like to play and exercise. Climbing is a particularly favored past time. Ensure that they have plenty of opportunities to explore and ascend their habitat.

If your hermit crabs are staying put and refusing to interact with their surroundings, learn why. Something must be wrong. Your responsibility is to determine whether the issue is physical or emotional.

Hearty Appetite

Ensure that your hermit crabs are eating and drinking appropriately, As befits animals of such small stature, hermit crabs do not eat huge amounts in a single serving. They will typically eat their fill daily, though.

Most hermit crabs like to eat at dusk. This is when, in the wild, they would emerge from hiding and start scavenging. This schedule will instinctively be carried over into captivity.

Hermit crabs will usually emerge from the substrate and eat a meal. This is especially common if you have served something tasty, with an appropriately appealing scent.

If your hermit crabs skip a meal, they may be waiting to eat later, when it’s a little quieter or darker. Do not let this behavior go on indefinitely, though. Like all animals, hermit crabs lose their appetite when sick.