Mary is a hermit crab owner advocating proper care for these often misunderstood creatures.
Old Wisdom and New Information
It has been long thought by many people that a land hermit crab in captivity requires little more than a small cage, a shallow water dish with a sponge, food, gravel, and a few things to climb on and hide in. Over the years, much research has been done, and it's now known that they require more specialized care than traditional wisdom tells us. Sadly, many pet stores and beach shops still stick to the old methods with very little change and pass this misinformation on to their customers.
Land hermit crabs have specific needs as far as space, heat, and humidity. They are social creatures, and do much better in groups. Initial setup of a proper crabitat can be pricey but there are ways to save money. The good news is that once you have a properly set up crabitat, long-term care is relatively inexpensive. Hermit crabs can live for decades in captivity if they are properly cared for.
Critter carriers and wire cages are not suitable for crabitats!
Plastic critter carrier and wire cages are too small and cannot hold in heat and humidity! Additionally, wire cages rust and crabs can break legs trying to climb them.
Tank and Substrate
A properly setup and maintained home for your crab is essential to your hermit crab's health and well being. Avoid using anything metal in your crabitat, as it can quickly rust in the humid environment. Rust is toxic to hermit crabs. Painted items should not be used either, as paint is also harmful. Colored plastic items are usually ok, as long as the color is part of the plastic and not painted on.
Glass aquariums meant for fish are the best choice for a crabitat. Glass tanks make it easier to keep temperature and humidity at proper levels. Hermit crabs are social, but also need their space. Allow for a minimum of 10 gallons of tank space per crab, 15 if they are a larger, jumbo size. As an example, if you are planning on 3 crabs, you will need at least a 30 gallon tank. If your crabs are very small, you may get away with a smaller tank for a time, but you'll have to upgrade as they grow. One of the mistakes we made was getting too small of a tank, which meant we had to upgrade to a larger one. It's easier and cheaper, in the long run, to start off with larger than you think you'll need.
Glass lids are the best option, again for heat and humidity control, but other methods can be used. Some crabbers have used corrugated plastic (Coroplast) or plexiglass cut to fit successfully as well. A screen lid can only be used if it is modified by covering it in plastic wrap or something similar, but are best viewed as a temporary measure. Screen lids are usually made of metal, so watch out for rust! In the case of rust, replace the lid as soon as possible. Make sure to secure any kind of lid to the tank! Hermit crabs are adept at escaping if given the chance and could get injured as a result.
It's generally recommended for hermit crabs to have a 12 hour day and night cycle. A regular aquarium hood light is usually sufficient. If you are using a heat lamp as a light source, use caution. Heat lamps can make it difficult to maintain proper humidity levels.
A good substrate should consist of 5 parts play sand to 1 part coco-fiber. It should be a minimum of 6 inches deep, or 3 times the height of your largest crab, whichever is deeper. Play sand is easily found at most hardware stores. Coco fiber bricks are cheaper and go further than the loose version, but it does need to be soaked in water before use. Excess water should be squeezed out before adding the coco fiber to the sand. Eco Earth is a popular brand of coco fiber, and is the brand I use, but there are others that work just as well. Substrate should not need to be changed at all unless you have an emergency, like a flood, mold issue, or bacterial bloom. A properly maintained crabitat can help reduce the chances of one of these things happening, but they do happen occasionally.
Food and Water
Land hermit crabs need fresh water, salt water, and a variety of foods in order to remain healthy. Commercially available hermit crabs foods are not necessary and most contain ingredients that are toxic to hermit crabs. Copper sulfate and ethoxyquin are 2 such ingredients that are harmful. Avoid chemicals and pesticides, as well as table salt. Hermit crabs need a well-balanced diet in order to thrive.
Many foods can be given as is, others may need to be cooked. Any food needing to be rinsed should be done so in treated fresh water. Foods needing to be cooked should be made without butter or seasonings, but EV olive oil may be used. You may have many crab-friendly foods already in your home. When foraging for food outdoors, make sure it's in an area where no chemicals or pesticides have been used. Check health food stores, many safe foods can be found in the bulk section. Look online as well. There are sellers that are dedicated to providing safe and healthy food for hermit crabs.
- Eggs, boiled or scrambled, no seasonings
- Worm castings (manure), yes...they love worm poo! Found in most garden centers
- Greensand, a mineral mined from the ocean floor, can also found in garden centers and online.
- Fruits: strawberries, bananas, watermelon, honeydew melon, mango, cantaloupe, blueberries
- Veggies: carrot, cauliflower, broccoli, celery leaves, green beans, pumpkin, spinach (greens should be cooked)
- Seeds & nuts: Chia, flax, crushed sesame, walnuts, cashews. Nuts should be unsalted.
- Rolled oats, NOT the quick cooking kind
- Chicken, raw or cooked with no seasonings
- Chicken bones, break them open so the marrow can be eaten
- Seafood such as shrimp, salmon, tuna, lobster including shell (seafood must be cooked)
- Some fresh or dried plants and flowers, rose petals, rose hips, hibiscus, clover.
- Some wood and leaves: Oak, oak leaves, cholla, grape wood
There are also a variety of bugs that they can eat including as mealworms, crickets, grasshoppers, and bloodworms. These all should be given frozen, dried or canned with no added ingredients. These can be found easily at pet stores. Some crabs may prefer freeze-dried versions, others might like canned or frozen.
Your crabitat will need two pools of water, one fresh and one salt water. Both pools should be deep enough for your largest crab to fully submerge in. Water should be changed at least every two days. Some crabbers like to use bubblers in their pools. If you choose to use bubblers, water can be changed once a week. You will need to provide a safe way in and out of the water so they don't drown. Aquarium plants and vines or ladders made from plastic canvas work great. I actually use both, so that there are two ways in and out of each pool. That way if something gets knocked down or out of place, there is a back up. Some shells or pebbles in the bottom of the pools can also help to give a boost to smaller crabs. It's a good idea to double up the containers you use to lessen the chance of flooding should one of the pools develop a crack.
Contrary to popular belief, sponges are not necessary in the pools and can actually harbor harmful bacteria. It's long been held that they need the sponges to drink from, but in reality, they do not. Hermit crabs will readily drink from their pools without the need for a sponge.
Fresh tap water should be treated with a water conditioner that removes chlorine and metals as well as chlorine and other harmful components. Seachem Prime is one such recommended brand, 2 drops per gallon of tap water or 1 drop for smaller amounts of water. According to the manufacturer, the ammonia and nitrate binding properties only last for 48 hours. If you are preparing gallons ahead of time, Prime will need to be added again before putting the water into the pools. My routine is to prepare the gallons ahead of time, then add an extra drop to each pool when changing the water. Tip: Don't remove the foil from the top of the bottle. Use a toothpick to poke a small hole so it will come out in drops.
For a saltwater mix, you will need ocean salt; many crabbers use Instant Ocean Sea Salt. There are other brands as well, just make sure it is a marine grade salt. Treat with Prime as for fresh water, then add 1/2 cup Instant Ocean per gallon. Mix it well or you will see settling of the salt. It can help to start with warm water as the salt will dissolve easier.
Temperature and Humidity
Hermit crabs come from tropical environments and need stable levels of heat and humidity. Optimum levels vary somewhat among different species. I'm most familiar with Purple Pinchers (Coenobita Clypeatus), so the levels talked about here are geared toward them. You may have to do some research if you have another species of hermit crab.
For all species, you should have a thermometer and a hygrometer to monitor levels. Combo units can be readily purchased, digital units are generally considered to be more accurate than analog versions. You may need to calibrate your unit.
Tank temperature should be around 80 degrees. Heat can be provided with a heat mat, commonly called an under-tank heater (UTH). For hermit crabs, a UTH should NOT be placed under the tank! It should go on the side or back of the tank, on the outside. Ideally, it should be large enough to cover the back of the tank where the substrate does not touch. The goal is to heat the air in the tank, not the substrate.
Proper humidity is very important to the health of your crabs, aim for about 80% humidity. Land hermit crabs breathe through modified gills that must stay moist. A dry crabitat will cause their gills to dry out, leading them to slowly suffocate. A properly moist (but not saturated) substrate and proper lid both help to maintain humidity. Avoid misting the tank! Over misting can make the substrate too moist and can lead to floods. If you need to raise your humidity, moistened moss pits (a plastic container of moss) can help, and crabs love them. Some crabbers will also use bubblers in the water pools; they break the surface tension of the water adding more moisture to the air.
Your hermit crabs will need plenty of natural shells to change into as they grow. It's important to have at least 3-5 shells PER crab. Not enough shells can result in shell fights. It's equally important that shells be of the right size and types for your crabs. Shells should not have any jagged edges or holes. Clean shells before offering them to your crabs by boiling them in crab safe water. Let them cool before adding them to the tank. You can also give them a swish in a little crab safe salt water mix; the salt seems to entice them to the shells.
Please avoid painted shells, paint is toxic to crabs! This includes any shells that may have clear glazing. While they may look fun and pretty, they are harmful to your crabs. Hermit crabs like to modify their shells and will actually eat some of it. If the shell is painted, they will ingest that as well. If you do acquire a crab already in a painted shell, do not try to remove it from the shell manually! This is extremely dangerous for your crabs, as they may let themselves be pulled apart before they'll let you take them out of it. The best you can do is to offer a good variety of natural shells, and let them change when they're ready.
Shell size should be determined by measuring inside the opening of the shell, not the entire shell. Measure the opening of the shell the crab is in and offer shells that size and somewhat larger. Sometimes they will change shells just because they want to, so they will need a few of the same size. Bigger shells are needed to accommodate for growth.
Look mainly for shells with round or D-shaped (oval) openings, as they are preferred by most hermit crabs. Overall, different species tend to prefer different types of shells, but it's still good to offer a variety. Individual crabs will have their own ideas of what they want to wear. For example, purple pinchers as a species like round openings, but some individuals may want a D-shaped opening. Some popular types of shells with round openings are Turbos, Pica, and Murex. D-shaped include Babylon, Conch, and Whale's Eye.
Climbing is Fun!
Choosing items to decorate your crabitat is another important consideration for the enrichment of your crabs. Hermit crabs are avid climbers. The will try to climb on everything, including the silicone in the corners of their tank! Mine have done that on more than one occasion. While they are social, they still need alone time so hiding places are a must as well. Here are a few common ideas for tank decor.
Unpainted coconut huts (real or plastic) make great hiding places. A cheap and easy alternative is a plastic container turned upside down, with a hole cut for a door.
Plastic aquarium plants and vines dress up the crabitat, and give your crabs something to climb. Make sure they don't have any exposed metal. For decor like bendable vines that have metal inside of them, monitor them closely. If any metal becomes exposed, remove it. Live plants should be avoided. Some are toxic, but even those that aren't will most likely not last long. Hermit crabs can be destructive and make quick work of destroying a plant. Root systems for plants that do survive can also interfere with a molting crab.
Hammocks meant for reptiles also make a great addition for climbing. Just make sure its made of a crab-safe material.
A "moss pit" is just some sort of container filled with moss. Crabs love to hide and sleep in it. They will even eat it. The moss can either be dry or moistened. A moistened moss pit can help add humidity if you are having trouble getting it to optimum levels. Not all mosses are crab-safe however. Sphagnum moss and pillow moss are two examples of safe mosses. Don't confuse sphagnum moss with sphagnum PEAT moss, sphagnum peat moss is NOT safe.
Wood items and branches make a nice looking natural decoration and provide more climbing space. Like moss, not all woods are safe. Safe woods include cholla, grapevine, cork bark, ash, and maple. Other woods like evergreen woods, laurel, and yew should not be used. Wood may mold or mildew in the humid environment, so check wood items regularly. You can lessen the chance of mold by cleaning the wood with a paste made of crab-safe water and the marine salt used for their salt pools. Scrub the wood thoroughly with the salt paste and rinse. You can air dry it, or bake in a low (200 degree) oven for several hours until dry. Use caution when baking and keep an eye on it. Let it cool before adding to the tank. If you still get mold, this cleaning process can be repeated as necessary.
You may also find it helpful to keep things like suction cups and zip ties for hanging and attaching decor. Self-stick plastic hooks are also handy. In my experience, the ones meant for kitchen and bath or outdoor use seem to hold up to the humidity better.
Plastic canvas from the craft store is another good item to have on hand. Ladders and climbing structures can be made with it. I use small zip ties to put pieces together or attach them to other things. It can easily be bent to hold a curve as well. Cut the plastic canvas to size and fold where you want the bend. Heat it carefully with a hair dryer until it's pliable; it usually only takes a minute or two. Hold in place until it's cooled. this is especially useful for making pool ladders.
Handling, Molting, and Activity
We all want to be close to and handle our pets, but hermit crabs are not like a dog or cat. Handling is stressful to them and should only occur when necessary for their care. Not only does it cause them stress, they need to remain in a warm and humid environment. Taking them out of the humidity of a proper crabitat makes it hard for them to breath and can damage their gills. Even if you do live in a naturally humid climate, it's still best to keep handling them to a minimum to avoid overly stressing your crabs. Crabs that are stressed might also give you a painful pinch!
Hermit crabs have a hard exoskeleton on the front part of their bodies, and they need to periodically shed that exoskeleton in order to grow in a process called molting. They will dig into the substrate to do this, building themselves a cave where they can safely molt. This process can take weeks or even months. Generally smaller crabs will molt more often, while larger crabs might molt less often and take much longer. Each crab is different though, and there's no way to predict exactly how often an individual will go through a molt or for how long. Do not go looking for or dig up a molting crab! Doing so could harm them, so they should not be disturbed.
Land hermit crabs are generally nocturnal animals. They can and do come out during the day, but you likely will find that much of your pets' activity will happen at night when the rest of the house is asleep. Some crabbers set up cameras to record nocturnal activity. This can be a great option if you want to see what your hermits get up to while you're sleeping.
As you can see, there is quite a bit more to keeping pet hermit crabs happy and healthy than just a few inexpensive care items, and it can seem a little daunting at first. However, if you are willing to put in the expense and effort they need to thrive, hermit crabs make fascinating and rewarding pets.
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This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
© 2017 Mary Camley
Mary Camley (author) on January 13, 2019:
Personally, I wouldn't chance leaving them overnight in a box if at all possible. Their gills need the humidity of a proper set up.
Keilla on January 13, 2019:
Can crabs stay in their cardboard box overnight before being moved to their tank?
Mary Camley (author) on September 16, 2018:
As long as you have the proper set up with adequate tank space, deep enough and the right kind of substrate, and the crabs bury themselves like they should, a quarantine tank isn't strictly necessary. That being said, it's still not a bad idea to have a quarantine set up for emergencies. Even with a proper set up, crabs can sometimes molt on the surface of the substrate. In the case of surface molts, it's necessary to isolate them from other crabs for their safety. Crabs may also need to be isolated if the main tank conditions aren't optimal, such as too shallow or improper substrate, or not enough tank space for the number of crabs.
LR on September 16, 2018:
Do you need to buy a quarantine tank for molting crabs? or can they stay in the same cage when molting?