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Crabs

Biology

Crabs are crustaceans and belong in the same group of animals as shrimps, lobsters and wood lice. Most of the group lives in water, often seawater, but a few have taken to living on land. Some of these species make very good pet animals. The types considered here are the hermit and rainbow crabs that live on beaches and further up the shoreline. Like their other crustacean cousins, crabs have a hard exoskeleton that is further toughened by having the mineral calcium carbonate de- posited in the tissue. This tough armour protects the animal from potential enemies and harsh conditions in the environment. Also typical of crabs, including those kept as pet is the possession of a pair of pincers. Most of these pet crabs will have one pincer larger than the other. In hermit crabs the large one is used to block off the entrance to the shell, while in fiddler crabs it is uses as a signaling device. As the crab grows it will moult its outer skin periodically. The first signs are often a refusal of food and increased aggressiveness. On no account should it be touched or interfered with. It will cast off the old skin and the emerged crab will often have re-grown any legs that have been shed. The crab will be very soft and may take a day or two to harden off, during which time it will not feed.

Housing

The permanent cage need not be large, about 30 cm x 20 cm x 15 cm being the average volume for an animal with a body size of about 6 cm. The cage should be set up in a manner similar to the diagram overleaf. A heater should be installed to provide a background temperature of between 20ºC and 30ºC. This is best done with an HabiStat mat or strip taped to the inside of the back wall of a wooden cage or either side if the wall is glass or plastic. Make sure the mat acts like a radiator, so very little of it should be below the line of the substrate. Much of the success achieved in keeping crabs will come from the skilful manipulation of ventilation. Some of these animals require highish humidity others like it much dryer but none can stand stagnant conditions. Fresh air moving into the cage is essential. Use the upward draughts caused by heated air rising to flush out the cage and drag fresh air in. A light misting with a hand sprayer will provide the 40% to 80% humidity required. Some species will require the substrate to be damp but not wringing wet. Look in the literature for details of the particular species being kept.

Husbandry

Most species will live in groups. Many will want to hide for most of the day so shelters should feature in the cage design. These animals do not really like being handled, so if it is necessary to move them, coax them into a box that can be closed afterwards and then carry the crab enclosed. The pincers will give stray fingers a nip if allowed to, so care should be taken to avoid any unpleasantness. The other problem with crabs is that they will shed a limb if it is trapped and the animal can escape by leaving it behind! This is supposed to happen and no treatment is necessary for the small wound caused. A new one will grow over the course of the next few moults. In time the cage will begin to look scruffy as faeces and debris builds up. As everything recommended for the cage is washable or disposable, a good clean out is easily done. The cage set up advised in this leaflet is practicable and can be made to look pleasing to the eye. It can be made to look quite natural even without using live plants, which are best left until some experience is gained. In any case, some of the very informative books on Crustaceans in general and crabs in particular could be investigated.

Food & Feeding

These crabs are not at all fussy about their food and will eat almost anything edible. Feeding pet crabs is easy and the best foods seem to be fresh fruit and vegetables with a little protein such as raw fish. Alternatives to try could include the dry pelleted diets or the frozen fresh meat preparations used for reptiles. Food is sensed by smell, and then grabbed with the pincers. Pieces are torn off and fed to the mouth. Crabs will test all sorts of material for food. They will certainly try all the items in the cage so do not be surprised if you see evidence of nibbling. This habit precludes the use of live plants in the cage, as they will be decimated and look very scruffy. Feed the crabs two or three times every week with enough to be eaten in about a couple of hours. Do not to leave an excess of uneaten food in the cage as it will quickly decompose and pollute the cage. A large water dish kept full of fresh water should always be available. The crabs should be able to freely enter and leave the water via a suitable surface. A steep or very smooth water dish will hamper their activity and may even cause them to drown!

Reproduction

To sex a crab, both male and female specimens are initially required. Upon inspection, the tail region is narrower in males and females are sometimes found to be carrying a brood of developing eggs. Some male fiddler crabs will also have a larger 'signaling' pincer than females. Breeding is not really a feasible option. Access to seawater is required and even then, the larval stages will prove difficult to rear.

Health & Disease

Crabs live for quite a few years in nature but as many will already be adult when purchased, no real estimate of life expectancy as pets can be made. They do not suffer from many diseases and veterinary attention is rarely needed. Good practice, hygiene and first aid will probably deal with rest. If real disease or injury is discovered, a suitable vet may of course, be consulted. Pet crabs do not pose a real threat to human health. All the normal hygiene precautions regarding humans and animals should, however, be observed.