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Do Hermit Crabs Eat Algae?

Hermit crabs are one of the more interesting members of the crustacean family. Other crabs grow their own protective shells to guard themselves against predators, but hermit crabs instead commandeer vacant shells. As they outgrow their old shell, they will actively seek out a larger one to make their home in. This characteristic, combined with bold coloration and their usefulness in keeping the tank clean, makes them a common addition to saltwater aquariums.

Wild Hermit Crabs
- Hermit crabs, like most other crabs, are scavengers. They live primarily on reefs and in intertidal areas, where the natural circulation of the water brings food to them. Their primary food source is algae, but they are opportunistic scavengers and will eat anything the tide brings their way. This includes larvae and small fish, worms, carrion, fish eggs and even the feces of other species. The small size of most hermit crabs allows them to feed and gives them shelter from predators in spaces that other creatures can't enter.
Crabs in the Aquarium
- Although most hermit crabs are small, they are voracious scavengers. This makes them a common addition to saltwater aquariums, as a valued member of the "cleaning staff" as well as a fascinating pet in their own right. In suitable numbers, hermit crabs will keep a tank largely algae-free, partly by eating it and partly by consuming nutrients that otherwise would encourage algae bloom. Their diet in an aquarium will typically include dead fish and surplus fish food. If a given tank is unusually clean, it may be necessary to provide the hermits with a dietary supplement such as seaweed.
Preferred Species for Aquariums
- There are many species of hermit crabs in the wild, but a few are more commonly used in aquariums because of their coloration, their efficiency as cleaners and their relative lack of aggression. The striped hermit, or Halloween hermit, has attractive red and orange coloration and is docile. The red reef hermit and red-striped hermit average about 1 inch in size, and are good choices for most aquariums. The blue-legged hermit, scarlet hermit and blue-eyed spotted hermit are also attractively colored, good scavengers and reasonably safe aquarium mates for your fish.
Special Considerations
- Hermit crabs are opportunistic feeders. Given the opportunity, they'll happily catch and consume your tank's other inhabitants, so make sure they're a lot smaller than your fish. Provide them with a lot of hiding places in the tank, which will make them feel at home. Also be aware that any hermit, even the most docile species, will battle its peers to the death if new homes are scarce. Avoid unnecessary losses by providing a large supply of shells in various sizes.

Animals & Science