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Choosing a Hermit Crab

By: Dr. Dawn Ruben

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Hermit crabs are hardy and undemanding pets that many people seem to buy on impulse. Although their name suggests a desire for solitude, the reverse is actually true: They thrive best when housed in groups and require proper temperature and humidity. Well cared for crabs can live for 6 to 15 years but many live only for 6 to 12 months.

History and Origin

Hermit crabs are a type of arthropod, which is one of the largest groups of animals, containing insects, spiders and lobsters. They have jointed limbs and a hard outer covering, called an exoskeleton. Crustaceans can be differentiated from other arthropods by two sets of antennae instead of one. Crustaceans are further divided and the order decapoda includes crabs, lobster and shrimp, all with five pairs of legs.

There are currently about 6000 species of crabs and 800 species of hermit crabs. A true crab has a short abdomen with a large hard shell. Hermit crabs are not true crabs. They have a long abdomen and do not have a hard covering, requiring them to use a leftover snail shell for protection.

In the wild, hermit crabs spend their days under tree roots, leaves, burrow, branches and rocks. They live in large groups and are active in the cool nighttime. Found all over the world, there are only two species found commonly in the pet trade: the purple claw crab (Coenobita clypeatus) and the Ecuadorian crab (Coenobita compressus). The purple claw crab is found in south Florida, the Caribbean and West Indies. The Ecuadorian crab is found along the west coast from Baja, California to Chile.

Appearance

Hermit crabs have five pairs of legs, each with different uses. The first pair have powerful claws with the left one larger than the right. The left claw is used for climbing and defense. The right claw is used for eating and climbing. When the crab retreats into his shell, the left claw is used to block the shell opening.

The remaining four pairs of legs are peripods. The second and third pairs are used for walking. The second pair has a weak ability to detect food. The fourth and fifth pairs are very small and never appear outside the shell. These legs are used to hold the crab inside the shell and to maneuver while walking. There are three pairs of small appendages around the mouth called maxillipeds used to grasp and tear food, to hold food in the mouth and to groom.

Hermit crabs have gills that must be kept moist to survive. These gills are smaller than the gills of aquatic hermit crabs, and if the crab is kept underwater too long he can drown. It is actually recommended that hermit crabs only be submerged during their weekly baths.

Hermit crabs use uninhabited snail shells to protect themselves from predators and help prevent water loss. Each crab needs to be provided with two to three extra shells for future molts or housing changes. The opening of the shell needs to be round and about 1/4 inch larger than the shell the crab currently lives in. If your crab cannot retract into his shell, he needs a new one.

Aging a crab is very difficult and determining the sex of a crab is just as hard.

The most commonly available crabs are about 2 inches in size. The purple claw crab is the most popular pet crab and can weigh up to 1/4 pound with very strong claws that have been known to snap a pencil. The Ecuadorian is much smaller and only weighs about 1 ounce when fully grown.

Behavior

Hermit crabs are social creatures and do better in a group. They are nocturnal animals, active at night and least active around noontime. Crabs don't bite but can pinch, even drawing blood. They are good climbers but can be clumsy and pointy toes can get snagged on carpet, drapes or upholstery. It is best to prevent aimless wandering. If wandering is a must, make sure your crab is supervised at all times.

Hermit crabs grow by shedding their exoskeleton. During molting, the crab usually remains in hiding. Many bury themselves in the substrate and may remain buried for up to a month. Molting crabs are very vulnerable and can easily dry out. Young crabs molt several times a year. As they age, molting may occur every 12 to 18 months. Do not disturb molting crabs.

Hermit crabs keep themselves quite clean but do need weekly baths to remove sand and dirt. Place your crab in a small bowl of tepid, dechlorinated water for just a few seconds. This allows debris to dislodge and helps moisten the gills. Crabs make a variety of sounds, such as whirring, croaking or chirping and communicate with their legs. Aggression can occur, especially pushing contests with other crabs or fighting over shells. The purple claw crab can be a little ornery and pinch but the Ecuadorian crab is considered sweet and trusting.

Feeding

Hermit crabs like varied diets and enjoy trying new foods. Various commercial foods are available such as cakes, meals, canned moist food and dry granules. If dry food is offered, the food may need to be moistened with water. Always have food available and placed in a dish. Moist food should be replaced daily to prevent decay and spoilage. Crabs do not always eat every day and your crab can safely go up to a week without eating.

Hermit crabs require calcium in their diet. A cuttlebone used for birds will provide sufficient calcium. In addition to calcium, hermit crabs appreciate fresh fruits and vegetables, especially grapes, raisins, lettuce and peanut butter. Live or dead insects, lightly salted popcorn and chicken bones have also been offered to crabs.

Hermit crabs require access to fresh water placed in a shallow dish no more than 2 inches in depth and at least 5 inches across. Make sure the water is no deeper than the crab's shell since hermit crabs can drown. In addition to fresh water, hermit crabs need salt water offered at least once a week, especially the Ecuadorian crabs. Salt for use in fish aquariums is required. Table salt can be fatal. If you find that your crabs do not drink the salt water, mix up a new batch with less salt.

Housing

Even though hermit crabs may appear small, they require room to roam. A glass aquarium or hard plastic cage makes an excellent choice. A 10-gallon aquarium works well for a family of two to three medium sized crabs. Goldfish bowls, despite living in them in pet stores, do not make good housing for hermit crabs. These critters are escape artists and a strong solid lid is required, though some ventilation needs to be provided.
Hermit crabs require warm humid environments to thrive. Temperature of the enclosure should be 70 to 75 degrees Fahrenheit. In cold times of the year, heat support, such as with an under tank heating pad, will be needed. It is important to use an aquarium thermometer to monitor the temperature. Hermit crabs do not require special lighting but do need 55 to 65 percent humidity. In a properly warmed environment, a large dish of water will produce sufficient humidity through evaporation as long as the terrarium is covered with a solid lid. Misting the cage daily with lukewarm water can also help keep humidity up.

The bottom of the enclosure needs to be covered with appropriate substrate, at an appropriate depth. Aquarium gravel used in fish tanks or high quality sand works well. It is very important to provide enough substrate to allow your crabs to burrow. For jumbo crabs, that may mean 7 to 10 inches of substrate. Small to medium crabs need 4 to 5 inches.

To keep your crabs happy and healthy, provide hiding places and items to climb on. Rocks, driftwood, shells, etc. can be used to climb. Broken ceramic flowerpots partially buried in the substrate make a great cave. Plastic and live plants can also be added to the enclosure but be careful with live plants – hermit crabs tend to enjoy destroying and shedding them.

The cage and accessories should be cleaned weekly and the substrate replaced at least every 3 to 6 months.

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