All hermit crabs need a shell for protection. No hermit crab will keep the same shell for its entire life, so it’ll periodically change its shell based on its adjusting requirements.
Hermit crabs will change their shells after molting, as a molt is often associated with growth in size.
If a shell has been damaged, a hermit crab will look to jettison and replace it. Hermit crabs may trade shells if dominant conspecifics challenge them for a more desirable shelter.
Some hermit crabs trade shells because they’re uncomfortable inside due to shards or spikes. Equally, the shell may contain parasites, such as mites. If the hermit crab is uncomfortable, it may change shells.
Also, stressed and unhappy hermit crabs may switch shells to enhance their level of contentment.
How Often Do Hermit Crabs Change Shells?
Young hermit crabs change shells near-constantly as they regularly increase in mass. As a hermit crab gets bigger, it needs a shell that can accommodate this evolution in size.
Once a hermit crab reaches adulthood, growth will slow down. The average hermit crab will molt every 12–18 months, vacating its shell to do so. Once the molt is complete, the hermit crab will need a new shell to accommodate its new body.
With this in mind, captive hermit crabs should always be provided with a selection of new shells. These can be kept to one side of the tank, accessible to all occupants.
Spare shells can be collected from the beach or purchased from specialist providers.
Why Is My Hermit Crab Changing Shells So Much?
When introducing a range of new shells to a hermit crab enclosure, expect the occupants to spend days trying different shells for size.
Animal Behavior describes this as a vacancy chain. Once the initial novelty of the new shells has worn off, hermit crabs should stick with one shell for a prolonged period.
If hermit crabs keep switching shells, this will be for one of these reasons:
1/ Size
As discussed, hermit crabs need to change shells as they grow. If a shell is too small for a hermit crab’s body, it may become trapped within this shelter.
Shells can be too big and too small. A hermit crab dragging a large, oversized shell behind itself will find its movements increasingly cumbersome and restricted. This will prevent the hermit crab from climbing and indulging in other preferred behaviors.
A shell is as important to a hermit crab as a house is to a human – arguably more so, as hermit crabs carry their homes on their back at all times. This means that finding a shell of appropriate size is essential.
2/ Discomfort
A hermit crab won’t be able to tolerate an uncomfortable shell, and neither should it.
Check the interior of the shell that your hermit crab is wearing. If you see any spines, spikes, or shards, these will lead to discomfort for the hermit crab.
As explained by the Journal of Experimental Marine Biology and Ecology, up to 149 species of parasites can impact hermit crabs. Mites can also infest a hermit crab habitat, causing no end of irritation.
Periodically clean hermit crab shells to minimize the risk of parasites. Brush the interior of shells with a toothbrush with distilled, filtered, or bottled water.
3/ Damage
Hermit crabs rely on their shells to protect them from predators and the sun’s UV rays.
The shell needs to be in impeccable condition to fulfill this duty. If the shell is cracked or otherwise damaged, the hermit crab will look to trade up.
Shells can be broken in various ways. Sometimes it’s wear and tear caused over time, but more often, it’s a consequence of impact. The hermit crab may have fallen while hanging from the ceiling of a tank or because you dropped it.
As per Marine Biology, a hermit crab will never willingly choose a damaged shell – it would prefer to find a smaller shelter in perfect condition. Remove any cracked or unsuitable shells.
4/ Competition from Other Hermit Crabs
As shells are crucial to hermit crabs, conflict for the finest vessels will invariably arise in a habitat. As explained by Behavior, this process can be an amicable exchange that benefits both parties, or it could become an act of aggression.
Usually, a dispute over shells will begin with one hermit crab tapping on the shell of another. This is a challenge for the right to use the shell in question. The incumbent of the shell may accept this challenge, or it may hide.
The two hermit crabs will wrestle if the shell owner decides to fight. The victor earns the right to the shell, while the loser must find an alternative.
Behavioral Ecology and Sociobiology said that aggression supersedes sheer size in a shell fight.
5/ Stress and Anxiety
If your hermit crab feels unsettled in its environment, it’ll do whatever it takes to settle any unwelcome nerves. Hermit crabs are often nervous and twitchy, so be mindful of their concerns.
If a hermit crab can’t pinpoint a reason for its unease, it may switch shells to feel better. If the problem lies elsewhere, switching shells won’t help, but the hermit crab will look to keep exchanging shells in the hope this will change things.
Temperature and Humidity
If your hermit crabs are too hot or cold or lack humidity in a habitat, they’ll grow increasingly uncomfortable. Hermit crabs may swap shells to alleviate discomfort.
Reduce this risk by maintaining appropriate conditions in a hermit crab habitat. This is known as the 80/80 rule – a temperature of 80OF and a humidity level of 80%.
Get a digital thermometer and hygrometer to maintain these levels.
Too Much Stimulation
Even if you devise the perfect habitat for hermit crabs, you’ll need to be mindful of the exterior.
Stimulation outside a hermit crab enclosure can upset the occupants. Your hermit crabs may start changing shells in the hope this will block more external factors.
Examples of stimulation that can upset hermit crabs include:
- Noise or scents that confuse the senses of hermit crabs.
- Excessive illumination, as hermit crabs prefer to relax in dim lighting.
- Other pets, such as dogs, cats, or birds, display predatory behaviors.
Hermit crabs flourish in a quiet room, away from other occupants, where they can be visited and interact with humans periodically. This will enable them to maintain a social relationship with their owners without growing overwhelmed.
Excessive Handling
Handling is important when you keep hermit crabs, as you’ll need to periodically relocate your pets for cleaning and otherwise interact with them. Don’t handle hermit crabs needlessly or excessively, though.
It’s impossible to handle a hermit crab without holding onto the shell. If your hermit crabs are determined to avoid handling, they may swap shells in the hope this will deter you from approaching them.
Boredom
Life can be pretty dull for captive hermit crabs. In the wild, hermit crabs have an entire beach to explore, so they amuse themselves by burrowing, climbing, and scavenging for food.
It may take a hermit crab some time to adapt to life in captivity, but they’ll get there with patience. The more you can replicate a wild environment, the sooner your hermit crabs adjust.
Keep your hermit crabs entertained. This means providing plenty of hiding places, climbing frames, and similar apparatus and offering different food every 24 hours.
If your hermit crabs are bored, they’ll look for another way to pass the time, which could include a rotation of shells. If you keep your hermit crabs amused, they’re likelier to stick with existing shells.
All hermit crabs trade and exchange shells after a molt; some will do so between these evolutions. Something may be amiss if your hermit crab constantly switches shells and appears unsettled.
