Hermit crabs are a trendy pet, but like all animals, they require humane treatment.

The Hermit Crab Association, which is an online group of enthusiasts, wants to dispel the notion that crabs are a "throwaway pet." So it posts detailed information on how to furnish a crab tank as well as how to feed, water and humidify the crustaceans.

The crabs are fairly soft-bodied. Each occupies an empty shell, both to protect itself and to conserve humidity. As a crab grows, it will periodically molt -- discard its outer "shell," which is called an exoskeleton -- and exchange its shell for a larger one. So it's best to offer several spare shells in its cage.

The crabs normally live in warm, humid coastal areas, so a pet habitat has to re-create that natural environment. A plastic tank needs to have high walls and a lid, so that the crabs, which are climbers, cannot escape.

To create adequate heat in a tank, owners can buy under-tank heaters. But the problem is not as great in Southern Nevada as in colder climates. Tank temperature should range between 70 and 80 degrees.

Shallow containers of prepared seawater and fresh water should be placed on the cage's bottom layer of dry sand or fine gravel. Table salt contains chemicals toxic to the crabs, so owners need to use a particular product to convert water into saltwater. Fresh water can come from the tap, but it must be dechlorinated before it's given to crabs.

The crabs use the water for drinking, bathing and humidity. The water should be changed daily, according to the Hermit Crab Association.

Crab aficionados vary on whether, and how often, to bathe a pet crab. One Web site recommends doing it twice a week in the desert, to promote hydration. Another school of thought claims forcing a crab to bathe is stressful, so let them bathe at will in the tank containers.

Sponges and moss can be placed in a crab tank to retain water and raise humidity, but check with a reliable crab information source on which types are suitable, and how often they need to be changed.

Pet stores sell a nutritional crab diet, in flake form. But crabs also eat a long list of other foods, including such human fare as bananas, carrots, celery leaves, citrus fruits, cucumbers, green beans, tomatoes, watermelon, popcorn, rice-rolled oats and commercial cereals of rice or wheat. Food in the tank should be replaced daily.

Many sites claim crabs enjoy company. But periodically they will fight over a shell.

If a crab starts losing limbs, it can be for several reasons. The stress of harvesting and travel is one. Dehydration is another. So is crab-on-crab aggression.

When passers-by tell crab vendor Nicole Suppa that it must be cruel for hermit crabs to live in painted shells, she answers that the shells, which are coated with nontoxic paints, are painted when empty.

The crabs do not breed in captivity.

By JOAN WHITELY