Scavenger
The hermit crab is called the "garbage collector of the seashore" according to the University of Michigan's Animal Diversity Web. It looks for food that has fallen to the sea floor, including dead and rotting material. It also feeds on particles of organic material from decomposing plants and animals. This makes it an important part of a natural seashore clean-up cycle.
Varied Diet
Hermit crabs will nibble on the flesh of dead animals that have fallen to the bottom of the sea, including dead worm matter. The hermit crab also likes to eat plants like sea plankton and algae. It will also chew on grass, leaves and rotting wood. They're also not above eating the feces of other creatures.
Food Intake
The hermit crab is not aggressive when it comes to food. It won't fight another crab to eat and can go 10 days without food or water. In the wild, a hermit crab venturing onto land will carry water in its shell so it always has a drinking source.
In Captivity
Hermit crabs as pets need a balanced diet. Crushed cuttle bone is commonly fed to pet crabs to give them a source of calcium. They also get small portions of carotene-rich vegetables like raw carrots and corn that help the crab maintain its orange-red color. The website hermit-crabs.com says the crabs prefer something different each time they eat. Some other options are oatmeal, rice, plankton, popcorn and well-cooked meat. The site points out hermit crabs love steamed shrimp tails.