hermits need shells of various sizes mainly depending on the variety of sizes of crabs that you have. crustaceans molt, and eventually they will outgrow their shells and require new larger ones to take over. if you do not provide shells for them, they will kill snails, conchs, or fight with other crabs for their shells. they will eat flake food, frozen food, live brine, various types of algae, and detrious. mine also eat seaweed sheets when i clip them to the glass. what they eat depends on the type of hermits you have...scarlets, red legs, blue legs, zebra's, there's a lot more to choose from.