Hermit crabs depend on their shells for shelter, hydration, safety, and protecting eggs.
Hermit crabs are rarely seen outside their shells. They quickly retreat when they sense danger or want to rest. That’s what earned them the name ‘hermit’ crab.
With that said, on rare and specific occasions, a hermit crab may leave its shell, or even appear to drop out of its shell if picked up or moved.
Hermit crabs will only drop out of their shells when sick, dead, or evicted by another hermit crab. On rare occasions, a hermit crab will also pick a shell that is the wrong size.
Hermit crabs have 10 legs. The 4th and 5th pairs are shaped, sized, and located perfectly to hold on to their shell firmly from the inside.
A hermit crab that seems to fall out of its shell should be monitored closely. There are several reasons for a hermie to exit its shell, and these are all driven by necessity and survival instinct.
How Do Hermit Crabs Stay In Their Shell?
Hermit crabs don’t fall out of their shells easily, even though conches are wet, slippery surfaces. Even in the wild, shells play an enormous role in a hermit crab’s life, directly influencing every aspect of it.
It is the main driving force behind most of the decisions they make. According to the Department of Zoology, the choice of shell even influences their growth rate and reproductive potential.
Hermit crabs are born without shells. They don’t arrive into the world with all they need to protect themselves and grow. Instead, they just have the necessary tools to hunt down and hold onto any materials they need.
Abdomen And Tail
Despite their name, hermit crabs are not true crabs because of how their body is designed. You may struggle to tell at a glance, since true crabs and hermit crabs are both:
- Omnivorous crustaceans
- Have 5 pairs of legs
- Have two strong pincers at the front
However, two key differences set hermit crabs apart from true crabs: their abdomen and tail. In particular, the tail extends and curls behind them, as opposed to underneath them. It is this long tail that fits into the spiraling depths of their chosen shells. That’s because the back half of their abdomen, unlike the powerful claws and front legs, are not covered by a strong exoskeleton.
Only the front of a hermit crab’s body is encased in this hard exterior shell. The rest of the hermie is vulnerable. By taking up residence in conches, hermit crabs can protect the more tender half of their body.
The natural curve of the abdomen helps the hermit crab avoid falling out. A hermit crab’s abdomen is quite soft and fleshy. It will always want to avoid having this exposed to predators.
Hermit Crab Legs
Another diverging aspect of hermit crabs is that their legs are not all the same size. In fact, they don’t even face the same direction.
The first 3 pairs are used for grasping things, eating, and moving around. However, it is the last 2 pairs that stay inside the shell at almost all times. This allows them to move around inside the shell and fix themselves in place. These back legs are tiny in comparison to the other 3 pairs. That gives them the flexibility to fit inside without issue.
Why Is My Hermit Crab Out Of Its Shell?
Take time to examine your hermit crab, so that you can decide how to intervene. Here are the reasons why hermit crabs will emerge from their shells:
Hermit crabs grow rather quickly. Unfortunately, their exoskeleton, the rigid armor that protects them, does not grow with them. To ensure continued growth, they will exit this tough exterior, shedding it almost as a snake sheds its skin. They will then begin to form and develop a new, bigger one.
This cannot be done inside of their conch. Instead, the hermie will leave its home behind and exit its skin. It will then bury itself in the sand. In this tightly-packed shelter, it will go through the process of growing a new exoskeleton.
This is a biologically complex process that is easily the most stressful part of a hermit crab’s life. They do it every 18 months, on average. Smaller hermit crabs will molt even more frequently. This is also how they regenerate any extremities which they have lost. Molting can take several weeks, or even months, for larger hermit crabs.
You can tell when your pet hermie is about to start molting. It will eat and drink more, storing energy and nutrients for hibernation. It will spend its days in a sort of stupor or lethargy. Its eyes will take on a cloudy look reminiscent of cataracts and take on an ashy or pale color.
If your hermit crab falls out of its shell at this time, it was going to leave it for a short time anyway. Once it’s regrown its new skin, it will return to its conch.
Hermit Crab Shell Evacuation
These carapaces are vital to a hermit crab’s continued wellbeing. They offer not only physical protection from predators, but also shelter from the sun. They even provide constant hydration due to the water that hermit crabs keep inside. If it chooses to evacuate, it may be because:
Shell Is Worn Out
Their shells must be in prime condition to be efficient homes. Wear and tear may degrade its living conditions, or the home may lack the volume needed to hold the hermie. In this case, a hermit crab will relinquish this home in search of another, more suitable home.
Shells may also be pierced, broken, or deteriorated to the point where they can no longer hold water. At the least, it may be unable to maintain sufficient humidity levels (between 70-80%, whew). These shells will be cast aside.
Hermit crabs have specialized gills that allow them to breathe by absorbing water molecules from the air around them. This explains their need for high humidity. If the shell becomes too dry, it will asphyxiate.
Shell Is Unsuitable
Hermit crabs have various criteria for choosing a shell, and won’t settle for just the first available conch that they find. According to Washington State University, hermit crabs will evaluate and select only the conches they expect will offer increased protection.
However, they must still be light enough to maintain agility and mobility. If a hermie chooses one shell and finds that it doesn’t actually serve its needs, it may leave to find another.
In rare circumstances, a hermit crab may also develop a skin infection, due to fungus or bacteria. This will cause a hermit crab to exit its shell temporarily. It does not feel comfortable inside, especially if the affected area is next to its abdominal area. These rare occurrences are usually corrected during the molting process.
Hermit crabs live in colonies of dozens, and even hundreds, of other hermit crabs. They have a collaborative society, sleeping together in huddles to keep warm. They even hunt for food together. However, there is one aspect of their society that may seem rather harsh to humans.
Hermit crabs are known to lie in wait for an opportunity to seize shells and claim them as their own. This may be as simple as stealing it when its former occupant is out examining another shell. Sometimes, it means battling and outright evicting an unlucky hermit crab, potentially leaving it homeless.
According to Hokkaido University, males were found to take less time to remove females from their shells than males. To improve their breeding opportunities, the males are safer with females.
This problem can be remedied by having a wide choice of available shells in the tank. When the battles start (and they will), no hermit crab is left to dry out in the sun.
Hermit Crab Died
A hermit crab may not be within its shell because it has died. If the hermit crab dies while inside, it will obviously become loose as neither its tail nor its legs will be grasping the inside.
Care should be taken before accepting death as the explanation. Always verify this before discarding or handling what you ‘suspect’ may be a dead hermit crab. It may be molting, or hidden away inside a shell, or perhaps has found a new shell without you noticing.
Even if you see a body slightly protruding from the shell, it may be a discarded exoskeleton. Evidence, like legs and antennae strewn about, isn’t concrete proof of a hermit crab’s demise. Hermit crabs have been known to rip off their own damaged limbs when in danger as they grow back after molting.
Dead hermit crabs will emit a strong, repulsive smell, akin to rotting fish. This makes it easy for you to tell if your hermie has expired or not. This same smell, coincidentally, will drive every nearby hermit crab into a frenzy. They will all scramble to get at its shell, and potentially eat its corpse as well.
What Happens When A Hermit Crab Falls Out Of Its Shell?
It doesn’t matter why your hermie is no longer in its shell. One fact remains: it needs to get back inside before too long. Aside from protection, the main reason hermit crabs use shells is to retain moisture and humidity.
While the high humidity is necessary for their gills to breathe, it also keeps their bodies moist. A hermit crab that spends an extended amount of time outside of its shell will desiccate. In other words, it dries out so much that it dies.
What To Do If Your Hermit Crab Is Out Of Its Shell
Your hermit crab may be unharmed and return to its shell. Offer appropriately-sized conches so that it can relocate when it is ready. Otherwise, you may need to assist your hermie to keep it alive.
Spray it lightly with dechlorinated water so that it stays hydrated. You can convince it to enter a shell by conditioning the available selection. This will include rinsing them in dechlorinated water and removing any objects that may be lodged within. Otherwise, that will deter a hermit crab from inhabiting it.
If your hermit crab has gone underground to molt, you might be shocked to see its empty shell just lying there. While molting, hermit crabs are at their most vulnerable, as their fleshy skin is mostly unprotected. They hide from other hermit crabs as they will not hesitate to engage in cannibalism if they find a ‘seemingly’ dead body.
If another hermit crab evicted the hermit crab, you should provide more shells in the future. This will help to reduce any conflict. Hermit crabs can fall out of their shells. However, they cannot stay out of them for long.