Breed: Land Hermit Crabs (Coenobita variabilis)
Temperament: social, non-responsive
Cost: crabs $7-$30 (set up $100-$200)
Lifespan: several months to years
Maintenance: low, though higher than one may expect
Recommended for: children over 10, apartments
Activity level: most active at night
Availability: widely available in pet stores
Land Hermit Crabs are part of a group of crabs that actually live the majority of their time out of the water. There are quite a few species of Land Hermit Crab distributed around the tropical waters of the globe although only one particular species, Coenobita variabilis, should be sold as a pet in Australia. Also called the ‘Australian Land Hermit Crab’ or often marketed as a ‘Crazy Crab’ it is the single legal source of hermit crabs for pets in Australia. Other species were once also available, however their sale is now illegal due to unsustainable pressures placed on the colonies from harvesting for the pet trade. The Australian Hermit Crab is not regarded as threatened as a result of their sale as pets.
Although very popular with children and regarded as a relatively low maintenance pet, hermit crabs do require a fairly exacting environment to survive. Don’t provide this environment and you will find that the hermit crabs won’t thrive and are likely to die in a relatively short time.
Found around the warm waters of Northern Australia, particularly the Northern Territory and Western Australia, the hermit crabs are a tropical species and require as close to precise tropical conditions in order to survive.
The variabilis species itself has a pretty wide variation in appearance. They range in size from a thimble to a tennis ball and in colour from pale sand through to reddish tones, depending on age. Hermit crabs will ‘moult’ as they grow, shedding their plate-like exoskeleton to form a larger one. Hermit crabs are not in fact true crabs and are more accurately called ‘false crabs’ because they don’t have a permanent, broad, flat shell. Like other crabs though, they are invertebrates and crustaceans, that is, they don’t have a backbone, have jointed legs and can live (at least partly) in the water.
Hermit crabs are so called because, instead of a permanent shell, they inhabit the empty shell of other sea molluscs and snails. Although the visible part of the hermit crab (its main legs, claws and head) are covered by the tough exoskeleton, the abdomen is actually devoid of this natural toughness and requires another animals’ shell to protect it. As the hermit crab grows within its own exoskeleton, it will eventually rupture out of this hard casing and retreat temporarily into its borrowed housing. At this stage the crab is very soft, fragile and most prone to stress. Once it has built up the energy reserves to move and its new exoskeleton has partially toughened up, it will leave its shell in search of another, larger model.
This is why it is important to ensure that your pet crabs live in the right environment. The growing process is traumatic and it’s only possible in a humid, tropical environment. Unlike many other crabs, hermit crabs spend most of their time out of the water. They scavenge for food in the ‘green belts’ behind the beaches, returning to the intertidal zone (that area where the ocean’s tides rise and fall on the beaches each day) to find replacement shells.
Setting up a tank isn’t hard and not very expensive either, but there are specific elements that are essential. Firstly, a glass rectangular fish tank is recommended. The size will determine how many crabs you can keep. An average tank, about 90cm long, will comfortably house around 15 hermit crabs. They are a social animal, preferring the company of other hermit crabs and will live happily in colonies. They like to explore their environment, so it’s suggested to provide as big a tank as possible. Smaller tanks are ok, but stock them with less crabs. Tanks are preferred over small, round bowls, they provide more surface area for the crabs to wander around.
Cover the bottom of the tank with at least a 5cm layer of clean, dry sand. Anything that mimics the crab’s natural habitat is best, so use cleaned beach sand if you can. The crabs love to climb and clamber over objects so put in pieces of dried drift wood, barnacles or other beach-like ornaments which will allow the crabs to scramble around. Hermit crabs are deceptively good climbers and can even escape by climbing up the silicon seals at the top edges of the tank. To prevent this and to help create a more stable, humid environment, place a lid over the top of the tank. Many tanks come with fitted, partially ventilated lids.
Humidity, nutrition, water and shells are all equally important to the hermit crab. Special food supplements are available where crabs are sold and these provide the essential nutrients required to help the crabs grow. The exoskeleton requires calcium carbonate in order to toughen during moulting phases. The supplements can provide this but barnacles, sea shells and the cuttle fish shell, often seen in bird cages, are also good sources for the crabs to chew on. Avoid placing any metal dishes in the tank. They detract from the look you want to achieve and it has been suggested that they can poison the very sensitive crabs. Use scallop shells for dishes to hold food and water. A little water dish serves two purposes, one is for drinking water and the other is to provide a small pool for the crabs to walk through, keeping their body moist when required. Hermit crabs drink fresh water but don’t use chlorinated tap water in the tank. Boil it first and let it cool. Partially bury the shells so the lip is level with the sand. Hermit crabs are natural scavengers, provide very small pieces of raw vegetable and meat daily to balance the diet and clean out any remnants of old food.
Natural sponges, dampened regularly will provide the crabs with another source of water and food and will also provide a source of water to help create a humid environment. Humidity isn’t possible without heat. Hermit crabs are cold-blooded and require an external, constant heat source. An ideal temperature range is between 24-27ºC. Under tank heaters work the best. These are buried under the sand and should be connected to a thermostat. Use a thermometer to monitor the temperature. Heaters are mainly sold for reptiles but work well for hermit crabs. Over-head lamps will only serve to dry out the tank, killing the crabs. Use a small water mister to spray a fine sheen of water on the tank’s sides to provide moisture for a humid environment. The crabs themselves don’t seem to mind a spray too.
Spare shells are vitally important. If you’ve provided the right environment, the crabs will grow. If they don’t grow they will die. Examine the crabs and provide enough shells for each to grow into during its next moult. Use those shells with round openings, not elongated slits. The hole of each subsequent shell should be about 1/3 to ½ as large as the crab’s current one. Just scatter the shells around the sand. Once the crabs have regained their strength after moulting, they will hop out of their old shell and search around for another that fits. Keep the old exoskeleton in the tank, it is a source of nutrition and the crabs will eat it.
Prices vary with size. Expect to pay around $7 for small crabs and up to $30 for the very large ones. In their own habitat, hermit crabs can live for many years, the largest ones being probably over ten years old. Large ones are not often sold in stores, as they are not regularly harvested so as not to impact greatly on the populations. We would suggest not purchasing large crabs. It will only encourage collectors to retrieve more in the future. A full tank set up will range from around $100-$200 depending on size and whether you purchase or collect ornaments yourself. A great pet for budding marine biologists, responsible children aged around 10 years or those with little room.
We filmed this segment with Vanessa Pike-Russell, a hermit crab enthusiast. Vanessa runs a website dedicated to providing hermit crab owners with plenty of information to help keep their crabs healthy.
Other interesting sites:
Crab Street Journal (an online hermit crab magazine)
The Land Hermit Crab Owners Society