I had several as a kid, fed them LITTLE pieces of raw hamburger.

I had a friend who financed his summer at the beach by distributing Hermit Crabs.
He said he rented an apartment, turned the heat on, imported 10,000 crabs and dumped them all out into the bedroom.
Every couple of days he'd throw a frozen turkey in for them to feed off of and pour five gallons of seawater into the kiddie pool.
At the end of the season he ate the security deposit, left the apartment as is and split.

they eat little but my advice is to make sure the sponge is wet every day!

Maintenance, Food, Nutrition, Humidity
Hermit crabs are essentially well known for being a low maintenance pet. They work well for kids and don't require as much work as a dog or a cat. They need to have bedding which should consist of sand or coconut bedding. They need to have as much humidity as possible. You can achieve this by providing a few shells with water. Make sure to also put sponges in the water dishes so that the crab can get out. You will also need to provide the crab with extra shells which are larger than its current shell. Crabs often molt, meaning that they shed all of the skin over their body. Then will then switch to another shell or stay in the same shell. About 4 inches of bedding is required for the molting process to take place.

You will also need some decorations to keep your hermit crab happy. You can provide the crab with fresh vegetables, lettuce and fruit. Their main diet consists of Hermit Crab food which is sometimes in a pellet form or a more powdered down form. You can buy hermit crab food online or you can purchase it in a pet store. You can also buy complete set ups which include a tank, food, sand and everything required to own a hermit crab. Hermit crabs live to be over 20 years old. They live a long time if they are cared for properly. The most important thing is to provide the crab with food and water. You always need to spray the tank with water also. Never use regular water to fill the water dish or sprayer bottle. Always use distilled water when topping off the water dishes. You can do this buy pouring regular water in the sprayer and letting it sit for 24 hours. This will eliminate the chlorine out of the water.

Hermit crabs have one large pincher which can do some damage to the skin. The larger the crab the more damage it can do. This is why I wouldn't recommend them for small children if they will be holding it. My hermit crab was very friendly and pinched me after I had him for 3 years. It seems as if you cannot train a hermit crab not to pinch. I would use caution with them around small children.

Hermit crabs can also have baths every few days. Dip the crab in distilled water to give it a bath. Do not leave it in the cup because they cannot swim or breathe under the water. They do enjoy baths, if given to them properly. You can also let them crawl around but never pull on them because it's legs will break off. Let the crab crawl onto a hard surface and grab the crab at that point. If you need to put the crab away, you can move whatever it is on into the tank until it crawls off. Sometimes they can be very stubborn. Just make sure it isn't something that could possibly hurt the crab or become a problem.

We had a few hermit crabs, I miss my favorite one "Green" we had him for almost 3yrs and he just died this past spring. Sucks they just don't last very long and aren't much of a pet ya know. They eat very little I would recommend just putting very lil food in the dish but as someone else said water is key. I used to put regular and salt water in my tank. Mine sometimes would rarely eat it seemed and others he would be in his dish all the time. Be aware that they molt and sometimes you think they are dead but they aren't. If they are curled up tight in there shell and seem dead they are molting so leave them alone LOL!

Had a big one pinch the tip of my thumb when I was in elementary school.  Managed to get a good piece of flesh and demonstrated considerable strength (and ability to inflict pain).