As hermit crabs are marine animals, it is often assumed they are strong swimmers. Despite having gills, and in many cases living underwater, hermit crabs are not natural swimmers.
Marine hermit crabs like the ocean floor. They climb to the surface using rocks and crevices or wait for the tide to ebb. Terrestrial hermit crabs submerge in water but do not swim for recreation. Land hermit crabs can only breathe underwater for a finite time, so they’re at risk of drowning. Land hermit crabs will not swim to the surface for air.
While all hermit crabs need water, aquatic or terrestrial, it is rare for hermit crabs to go swimming. If caring for hermit crabs, you must ensure that their exposure to water is managed appropriately.
Can Hermit Crabs Swim?
The anatomy of the hermit crab is not designed for swimming. If you take a look at the legs of a hermit crab, you will understand why. Hermit crabs have ten legs, including those topped with claws (called chelipeds). The remaining legs are called pereiopods. These are as follows:
- Front legs – a large and small claw, used for self-defense and scooping food or water into the mouth
- Second and third pairs of legs – used for walking. These legs carry the weight of a hermit crab’s shell and lift the abdomen from the surface
- Third pair of legs – stubby appendages used to get in and out of a shell
- Rear legs – grooming appendages used for cleaning gills and the shell
As you’ll see, of these ten legs, only four are theoretically helpful for swimming. The others are too short or cumbersome. Even then, the legs in the middle of a hermit crab’s body are not cut out for swimming.
Hermit crab legs do not have knee joints comparable to those of other animals. Their legs do bend forward and backward, though. This is why hermit crabs walk in straight, linear lines rather than scuttling sideways like other crabs.
Despite this, the limited mobility of hermit crab legs makes swimming difficult. The claws are of no help. The four rearmost legs are too short to generate any real propulsion. This only leaves the four walking legs, and even they cannot move freely in the water.
This all means that, despite living underwater, marine hermit crabs do not swim. Instead, they wander the floors of the seabed. Land hermit crabs, meanwhile, have no reason to learn to swim. They avoid entering water deep enough for this to become necessary.
Do Hermit Crabs Like to Swim?
Due to their physiology, hermit crabs do not find attempts at swimming pleasurable. This is why most hermit crabs remain in comparatively shallow water. While the Bulletin of Marine Science confirms that some dwell as deep as 713 meters, most stay within 450 meters.
Marine hermit crabs spend time on land occasionally. This is to search for food or a shell. They can breathe out of the water while their gills remain damp. They walk along the ocean floor reach land, though. Eventually, the tide ebbs enough to reach the shore.
Alternatively, these hermit crabs will climb their way to dry land. All hermit crabs are skilled climbers. They attach themselves to cliff faces or anything else they can grip. The hermit crabs then make their way to land.
There is little reason for hermit crabs to swim in the water. Most food sources for marine hermit crabs are found on the ocean floor. Hermit crabs will hunt sea snails for food and to occupy their shells. Hermit crabs feast on algae and corals found at the bottom of the sea.
Land hermit crabs have no reason to swim. They submerge in water, but never for long. Terrestrial hermit crabs drown if underwater for prolonged periods. Attempting to swim magnifies this risk. Land hermit crabs stick to shallow water, close to the shore.
Hermit crabs also place themselves in needless danger by swimming. They are at the bottom of the oceanic food chain. Swimming will lead to encounters with common predators. These include fish, whales, sharks, and octopi, according to Hydrobiologia.
Do Hermit Crabs Need Water to Swim in?
We have now established that swimming is not a priority for hermit crabs. Regardless of whether you bring marine or land-based hermit crabs into your home, they will not be keen swimmers.
This does not mean that hermit crabs do not need water, though. If you are caring for marine hermit crabs, they need to live underwater in an aquarium. If you adopt land hermit crabs, they still need a pool of water for bathing and drinking.
Water Needs of Marine Hermit Crabs
If you adopt marine hermit crabs, they must live in a saltwater aquarium. There is no way to successfully convert aquatic hermit crabs to land dwellers. These animals take their oxygen from the water and need constantly damp gills.
Captive hermit crabs still will not swim around the tank. Do not adopt these pets expecting such antics. They may climb reefs and traverse the walls of the tank occasionally. Most often though, your hermit crabs will keep all ten feet on the substrate.
Ensure that you understand the needs of your hermit crabs before placing them in water. Different breeds of hermit crab have varying requirements. Think about whether you want your hermit crabs to share their home with fish or turtles, too.
Hermit crabs are largely docile and can typically get along with most other animals. This is why many fish keepers bring hermit crabs into their aquariums as janitors. They will dwell at the bottom of the tank, keeping algae growth under control by eating it.
The same cannot be said of certain breeds of fish or turtle, though. These may view hermit crabs as an infiltrator at best and a snack at worst. The fact that hermit crabs do not swim should help them stay out of the way. The risk is always there, though.
Water Needs of Land Hermit Crabs
As discussed, land hermit crabs submerge themselves in the water on occasion. This means that, although hermit crabs do not swim, they still need a ‘swimming pool.’
How often your hermit crabs submerge in water depends on how humid their enclosure is. Always aim for 80% humidity, using a misting spray if necessary. If the humidity drops below this level, the crab’s gills dry out.
If your hermit crab is bathing daily, this suggests the habitat lacks humidity. Invest in a hygrometer to check this. Consider adding moss to the tank and wrapping the roof in Saran wrap to retain moisture.
In addition to dampening the gills, hermit crabs submerge in water for a range of reasons. These include:
- Filling the shell with drinking water, in case this is needed in future
- Bathing – hermit crabs loathe feeling unsanitary
- Removing parasites, such as mites, that have attached themselves to the skin
- Cooling off in hot conditions
A swimming pool is a must for land hermit crabs, in addition to a smaller bowl of drinking water. Be careful with this, though. Land hermit crabs cannot hold their breath indefinitely and drowning is a risk. 30 minutes is the longest most land crabs can last underwater.
Creating a Swimming Pool for Land Hermit Crabs
To create a safe swimming pool for land hermit crabs, you will need the following:
- A vessel deep enough for complete submersion – this will act as the swimming pool
- A one-gallon vessel for mixing pool water
- Bottled water or a water filter
- Marine salt to create appropriate salinity
- Apparatus to aid hermit crabs in leaving the swimming pool
To choose the perfect vessel size, measure your hermit crabs. Use a vessel that holds around one additional inch of water. This allows the crabs to submerge, but not find themselves in deep water. If you have multiple crabs of varying sizes, make multiple pools.
Apply your water to a jug until you have one gallon of water. Remember, this must be bottled or filtered. Conventional tap water contains toxins, such as chlorine and copper. These will poison your hermit crab.
Now, add your marine salt to this water. Half a cup of salt per gallon is usually ideal but check the packaging of your product. Never use table salt for salinity. This contains iodine, which again, is toxic to hermit crabs.
Once the salt is dissolved and the water is clear, it can be poured into your swimming pool vessel. Before applying this to your hermit crab habitat, you need to provide entry and exit points. Ramps are best for this.
You can pick up a plastic mesh online or from a hardware store. This is sturdy enough to hold the weight of hermit crabs and will not rust in water. The holes in the mesh are also ideal for a hermit crab to climb when getting in and out of water.
Can I Put Land Hermit Crabs in a Water Tank?
There could be a reason why a swimming pool is not possible in your enclosure. Perhaps the tank is too small. Alternatively, you may wish to supervise the bathing habits of your hermit crabs. As these animals are nocturnal, this is not always possible.
In these instances, you may wish to consider placing a land hermit crab in a watery aquarium for a spell. This can work, but it is fraught with danger. This is not a decision to take lightly. Remember, land hermit crabs will not swim in the water if that is your hope.
The biggest risk of placing land hermit crabs in an aquarium is the depth. There is no way of knowing how long a hermit crab can hold its breath. The longer it remains underwater, the more disoriented the crab will become.
This is especially likely in an aquarium filled with distractions. As per Behavioral Processes, prolonged white noise – such as a water pump – will dull the animal’s senses. Hermit crabs can forget themselves. Before you know it, your pet may be gasping for air.
Equally, consider the impact this will have on pre-existing inhabitants of the aquarium. Some breeds of fish can be antagonistic toward hermit crabs, even eating them. Also, resident marine hermit crabs may treat these new arrivals as territorial rivals.
Land hermit crabs can have fun venturing into an aquatic tank. They will have new terrain to explore and will enjoy eating algae. Keep this as an occasional, sporadic, and strictly short-term exercise, though.
Never casually place hermit crabs into a body of water and expect them to swim. Even aquatic hermit crabs will find this distressing.