Most people who have pets have kept a pet hermit crab at some point in their lives, or know someone who did-- especially if they vacation at the beach. Pet store workers often hear complaints that hermit crabs don’t live very long, or worse, customers encouraging children to get these pets because they don’t live very long and they require little care or upfront cost. The thing is, none of that is true. Hermit crabs can live for multiple decades and get to be the size of a softball (counting their shell) but few people realize just how much work has to go into properly keeping hermit crabs.
Hermit Crab Anatomy
All hermit crabs have antennae, eye stalks, and 5 pairs of legs. The first pair have claws (one small and one large) for picking up food and defense, the next two pairs are walking legs, and the last two pairs hold the shell in place. Despite the fact many live on land, hermit crabs also have gills and have to constantly keep them moist. All hermit crabs except for the Coconut Crab also have a hard exoskeleton on the front portion of their bodies, including the claws, legs, head, and upper abdomen. The tail, however, is entirely soft. This is the part that the crab must protect at all costs, and why it carries a shell from another animal on its back!
On a hermit crab’s 4th legs, if its female, are tiny holes called gonopores which are used in breeding. You can see these legs by placing the crab in a clear-bottomed carrier and watching underneath until they walk around. You’re not going to end up with babies if you house male and female crabs together, though, as they absolutely cannot breed without the ocean tides and currents. The downside to this, though, is that not a single hermit crab has ever been born in captivity. This means that all hermit crabs you ever see for sale have come from the wild, and this is a conservation issue that can impact an island.
To have as little impact on the environment as possible, I recommend checking online for local hermit crab rescues if you’d like to become a hermit crab keeper (AKA Crabber). Don’t beat yourself up too much if you’ve bought a crab from a store before this, though-- I did it before I knew better too. Just try to adopt future friends for your crab rather than purchasing them. It’s amazing how many rescuers there are out there. (When I had to move and could not bring my crabs, I gave them to a rescuer who kept a colony of over 100 that I found through craigslist!)
Hermit Crab Species
There are over 1,000 hermit crab species. Some live in entirely marine environments, some in freshwater, and some on land. The Coconut Crab is particularly famous as the largest hermit crab species in the world-- it is so big that it cannot find a shell big enough to fit its back when it becomes full grown, and so it grows a hard exoskeleton across all parts of its body as it ages.
The kind of hermit crabs that most people think about for pets are usually the species known as a Caribbean Hermit Crab, or Purple Pincher. They got this name because they have one small claw and one very large, purple claw while the rest of them is usually tan and orangey-red. They have somewhat round eyes on top of their stalks. The second most common species you will find is the Ecuadorian Hermit Crab, which is easily distinguished by its claws being less exaggerated in size difference, having a tan or brown body all over (including its claws), and having elongated eyes. There are several other species that are kept as pets by hobbyists but they are harder to find and usually have to be bought from a specialist. They all have different sizes, colors, claw shape, and eye shape. For the most part all species are kept about the same, but they each have a few preferences for substrate type, water sources, etc. so be sure to do a little extra research if you find yourself with a different species. The care sheet here if focused on Caribbean Crabs, as they’re the easiest to find and care for.
Hermit crab care is very similar to keeping a vivarium for amphibians or tropical reptiles. When they are young, you can start with as small as a 10 gallon tank and grow your tank as the crabs do. To keep it affordable, check thift shops, craigslist, etc regularly for old tanks, or wait for a big sale at your local pet store (some offer a $1/gallon sale seasonally). Place thermometers and humidity gauges in the tank- at multiple locations if your tank is large. The tank requires a daylight bulb and a temperature between 75 and 85F. Crabbers recommend 80F, and one should never go below 70F as it may trigger hibernation or illness. It’s also helpful to have a slight gradient in the tank temperature as hermit crabs are cold blooded and need to regulate their body temperature using their environment. To do this, in addition to the heat from the light, place an under tank heater (UTH) on the back of the tank. Why the back? It will not only warm the air in the tank this way, but placing a UTH under the tank can result in a cracked tank bottom if your tank sits on a solid surface, or will fall off after awhile if the bottom of the tank stand is open.
Humidity is the hardest thing to keep-- below 70% will cause damage to a crab’s gills (and a slow suffocation) and above 80% invites mold growth. The best substrate to prevent mold and encourage digging is a roughly 50/50 mix of sand and coconut fiber. Play sand from the hardware store is fine, but smell it to make sure it hasn’t been contaminated by oils from delivery vehicles. This substrate should be moist at all times- just enough to build a sandcastle out of. Fill the tank four times as deep as the crab is large (about halfway up a long tank, or one quarter of the way up a tall tank). Place moss in one enclosed space in the tank (a food storage container will do). Spray the tank as needed and the moss daily to keep the humidity up. If you use a mesh lid, plastic wrap held down with aluminum tape on the exposed portions will seal it well.
Crabs are great climbers, so make use of the height in your tank to give them as much vertical space as possible. Nets, branches, and other aquarium furniture from the reptile or fish aisles are all useful, or make your own with natural materials like jute twine. Coconut fiber backdrops are good for this too and can help hold in humidity. Whatever you do, don’t become attached to where you place something, as crabs are stubborn things. If something is in their way, they will walk over it or push it, rather than go around. Be sure to give them hiding places as well.
As Caribbean crabs live along the coast, they are accustomed to both fresh and salt water. Provide one shallow dish of each- the dish should be deep enough for a crab to soak in, but not so deep they will drown. If you have many sizes of crabs, put a sponge in the dish to help the littlest ones climb out. All water should be dechlorinated, and only use aquarium salt to make your water mix, never kitchen salt.
The easiest part of caring for hermit crabs is their food. They are omnivorous and scavengers, so as long as you provide them with a base of hermit crab diet, you can change up the rest of their diet daily. I gave them the scraps from preparing my own meals as well as foodstuffs I collected outside or scraps from other animals’ diets. (Always clean food thoroughly as any pesticides and fertilizers can hurt them). For added calcium, use a large shell as a dish or provide cuttlebone from the bird section at the pet store.
Molting & Shell Shopping
Like other arthropods, hermit crabs have to shed their exoskeleton to grow, or molt. When they do this, they are extremely vulnerable and other animals, even crabs from their own colony, will try to eat them. To avoid others, hermit crabs will dig deep burrows and stay underground to leave their shell, shed their exoskeleton, harden their new exoskeleton (they are literally soft-shell crab when they first molt), and then put their shell back on before digging back up to the surface. Sometimes you get lucky and the crab will dig a tunnel alongside the glass of the tank so you can watch the process. Molting can take months, though, so if you can’t see where they are, sometimes people mistakenly think that their crab died. Rest assured, you will know if your crab has died because it will have the unmistakable smell of dead fish. If you don’t smell that, it’s in there somewhere (unless it got eaten but you’d find its shell).
Hermit crabs change their shells regularly. Just like we get too big for our clothes, crabs need to constantly “shop” for new shells. Some are pickier than others-- but generally they prefer a shell with an opening that matches the size and shape of their large claw. This isn’t a tried and true rule, however, so it’s good to provide a wide variety of shells for your crabs at all times. Moe would change his shell several times in one day only to go back to his favorite colored shell, a bright green painted one he came home from the store in. Painted shells are bad for crabs, by the way, so be sure to take those out as soon as the crab has left theirs alone. The paint not only could contain toxins the crab might eat if the paint chips off (and this paint is often lead-based from China), but a painted or plastic shell is not breathable.
When looking for shells, there are a few ways you can go about it. One is to buy shells individually, which is what pet parents of full grown hermit crabs often have to do. If you have small crabs, though, the simplest way to buy shells is to purchase an assortment from the floral section of the craft store. Always be sure to sanitize the shells by boiling them in non-chlorinated water for about 15-20 minutes (add aquarium salt to help attract the crabs). Do this every couple months with the shells in the tank as well, whenever you do a deep clean, and use an old pot you don’t mind accidentally staining if you find out the hard way the shells were not clean.
Shells Preferred by Caribbean Hermit Crabs:
With patience and steady hands, it is possible to hold your hermit crab without gloves, even a large one. When picking them up, make sure your hands are clean and free of chemicals like soap, grab them by the widest part of their shell, tilt it back so they aren’t hanging out, and then place them in the palm of your hand. A crab will not pinch unless it feels threatened, such as if it feels like it is going to fall out of your hand. Once comfortable, they will walk around your hands to the edge, and place the other hand in front to give it a new part of “road” to walk on (this is called laddering). Don’t have them out too long without spraying them with dechlorinated water, or else their gills will dry and they will have trouble breathing. When transporting, do the same by filling the bottom of the carrier tank with substrate or a paper towel and spraying it with water. Put a towel over the carrier or put the carrier in a cooler to keep the crab warm and the humidity up.
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Ferrets and Friends, LLC has four writers bringing you information on a variety of topics from pets to wildlife, education to conservation, and from new developments in our business to information about our industry. Learn something new each week!