With ten legs and a soft underbelly, you would be forgiven for assuming that hermit crabs would prefer to keep their feet on the ground. Some hermit crabs willingly flip over and get stuck on their back.
Hermit crabs flip onto their back to sleep, molt, and protect their shells from rivals. Sometimes, hermit crabs fall while climbing and land on their backs, where they remain as the impact daze them. At other times, hermit crabs can get trapped on their back.
It’s important to learn when a hermit crab chooses to lie on its back and when it needs assistance. If the hermit crab can gain access to a solid object, it’ll use this as leverage to right itself.
If you find a hermit crab flipped on its back or stuck between decorations, help it turn over and get back on its feet. This is best done from a safe distance, using a flat foreign object to avoid being pinched.
Why is My Hermit Crab Laying Upside Down?
Finding a hermit crab lying upside down isn’t necessarily a source of concern.
It would be understandable to be concerned that a hermit crab lying on its back must be dead. Why else would it assume that position? Test this by placing sweet-smelling food nearby, as your hermit crab’s antennae will likely twitch, confirming it’s alive.
Some hermit crabs find it relaxing to lay on their back or are used to this position. Hermit crabs sold in beachfront gift shops are often placed on their back to give customers a better look at their potential new pet, so it may become a habit.
Avoid immediately picking up a hermit crab that is on its back. You’ll likely startle the hermit crab, who’ll instinctively pinch you. Try to assert why your hermit crab is on its back, so you know how to react.
Here are the most common explanations:
Insufficient Substrate
Many hermit crabs like to sleep on their backs, so they may flip over to assume this position for a doze. It’s rare for hermit crabs to sleep out in the open, especially during daylight hours. The habitat may lack substrate if you find your hermit crab in this position.
Typically, six inches of substrate is enough for a 10- or 20-gallon hermit crab tank. This will provide enough padding if the hermit crab falls while climbing, and more importantly, it will be deep enough for hermit crabs to bury themselves under.
You may need to apply more substrate if you have multiple hermit crabs. All the hermit crabs will be keen to bury themselves under the sand simultaneously, so there needs to be enough space for each one to have its separate territory.
The more hermit crabs you have, the more substrate will be kicked up by digging and playing. This can leave the substrate thinner than you anticipate. You’ll also remove some substrate during spot cleaning. So, always measure and replace the level of sand in a tank.
Preparing to Molt
As well as sleeping, hermit crabs flip themselves on their backs during molting. Adult hermit crabs molt every 18 months.
While most hermit crabs bury themselves under the substrate to molt, Invertebrate Biology explains how some only bury themselves in shallow sand.
The molting process is gradual, and you’ll notice some telltale signs before your hermit crab hides. Many inexperienced owners confuse molting with death, so ensure you understand the signals.
Alongside flipping onto its back, signs that a hermit crab is preparing to molt include:
- Glazed, glassy eyes and general lethargy.
- Eating more than usual to build a stock of fat.
- Bathing more frequently to store water in the shell.
- Digging to excess, as though creating a tunnel.
- The exoskeleton fades to a dull gray.
If you have the time and it’s safe, move your hermit crab to a private isolation tank ahead of molting. The hermit crab can rejoin its tankmates once the molt is concluded.
Falling from Height
Hermit crabs like to climb, and falling is a natural side effect of this pastime. Hermit crabs will climb anything scalable in a habitat, most notably the walls of a tank. It is not uncommon to find hermit crabs hanging upside down from a tank’s roof.
This behavior, in and of itself, is nothing to worry about. Just ensure that your hermit crabs aren’t trying to escape their habitat. If this is the case, something is amiss, and the hermit crabs are upset.
Climbing is often exhausting for hermit crabs, so they may fall at some point. This could happen midway through scaling a wall, or the hermit crab may lose its grip hanging from the ceiling.
The potential for falls is why shells and sufficient substrate are crucial to hermit crabs, and these two factors will protect your hermit crabs from significant harm.
However, a hermit crab may be dazed after a fall, and it will take a while to reorient itself.
Stress and Anxiety
Hermit crabs are easily spooked or startled and sometimes flip on their back to ease their anxiety. While hermit crabs have a soft underbelly, they sometimes feel more comfortable lying on their back.
If it needs to fight, lying on the back makes it easier for a hermit crab to battle with the chelipeds. It can pinch quickly, then retreat into the shell and out of harm’s way.
Hermit crabs can face conflict from rivals over shells. According to Behavior, hermit crabs that covet a rival’s shell challenge a resident to a duel by rapping upon the shell.
If the shell is flipped and covered by substrate, the aggressor can’t reach it and issue a challenge.
Trapped Between Two Objects
Hermit crabs like to hide, so rocks and similar decorations greatly add to a habitat.
Try to space these out strategically. While two additions close to each other make a great hiding place, your hermit crab may get trapped between them.
Consider that hermit crabs love to climb. Your hermit crabs won’t hesitate to clamber over one rock and onto another. If it falls and becomes wedged between the two rocks, it’ll be impossible for a hermit crab to move and get free again.
Sometimes, a generous conspecific will come along and help the trapped hermit crab. It’s likelier that the hermit crab will grow anxious and stressed, potentially shedding limbs in an attempt to free itself.
One way to get around this concern is by installing ramps and bridges between rocks and other decorations. This means your hermit crabs can negotiate the terrain with less risk of falling.
A ramp of sufficient size will also create space between items.
Can Hermit Crabs Turn Themselves Over?
If a hermit crab has flipped itself over, it may have done so on impulse without considering what comes next, which means it may be incapable of righting itself. Hermit crabs can turn themselves over but will need leverage to do so.
If a hermit crab has flipped itself close to an inanimate object, such as a rock, it can use this to lift its body weight. If the hermit crab is incapable of doing so, it may be injured or living in a shell that’s too large or heavy to negotiate.
If you find a hermit crab lying on its back, don’t immediately reach in and attempt to right it. It won’t understand your intentions and may panic, pinching you in self-defense.
Instead, find a flat surface – either a wide spatula or a piece of solid cardboard – and guide the hermit crab toward a solid object. See if the hermit crab can right itself. If not, consider manually flipping it if you’re sure this is what it wants.
