In nature, a hermit crab is omnivorous. This means that hermit crabs eat a little of everything including plants and meats. While they are in captivity as a pet, their diet should either be based on a commercial diet with crab food and supplements of natural foods, or a natural diet consisting of foods you yourself might eat. Whatever you feel is best for your hermit crab, they are both adequate to nourish your crab.
As far as commercial food goes, there are several different types of crab food. Ask your local pet store specialist which they would recommend. Crab foods come in pellets or granules. If you are planning to use pellets, they should be crushed into a powder, to make it more easily accessible for your hermit crabs, especially if you plan to purchase a small crab. You can feed other commercial pet foods like reptile food or fish flakes. Whichever you choose, commercial foods need to be supplemented by natural treats. Veggies and fruits are great supplements to a commercial foods diet. Cooked chicken is also a great thing to treat your crab to every now and then.
Commercial diets are very convenient and most are fairly well-balanced. However, the best diet for your hermit crab is a diet full of natural foods only. Fruits that may be fed include mango, papaya, coconut, grapes, and bananas. Veggies that are appropriate to feed your hermit crab are carrots, spinach, broccoli, and seaweed. There are many more foods that are available to feed your hermit crab on a natural foods diet. A care sheet containing all the available foods can be picked up at most decent sized pet stores. Avoid starchy veggies like potatoes as well as avoid dairy products. You might find that your crab likes sweets or salty junk food. This should be rarely given for snacks, as it is not good for the hermit crab anymore than it is for people.
Besides being fed, hermit crabs need calcium. Some ways to provide calcium for your hermit crab are cuttlebone, found in most pet stores in the bird section. This can be broken up or given whole. There are also calcium supplements that can be given to the hermit crab besides cuttlebone. Also, crushed oyster shell, coral sand, and cleaned crushed eggshells all contain calcium for the hermit crab.
Besides food and calcium, hermit crabs need water. Purified water is the only water that will do. Chlorinated water is not acceptable to give to hermit crabs because it can harm their modified gills, causing blisters on them if repeatedly exposed to it. Needed is a water dish large enough for the required natural sponge and for the hermit crab to soak in. Be careful to offer a place for smaller crabs to get out of the dish so they do not drown. This first water dish is to contain fresh water. There is needed a second dish that should contain salt water, for the hermit crab. They have access to the saltwater in their natural habitats. A sea sponge should also be placed in this container as well. Feeding and providing water for your crab is a vital part of the hermit crab’s survival. Research as much as you can where this is concerned, as hermit crabs are not just throw away pets.