Scarlet Reef Hermit Crab

With its bright red body and legs from head to tail and yellow eyestalks, the scarlet reef hermit crab is one of the most colorful members of the aquarium cleanup crew. Like other hermit crabs, it lives in empty snail shells to protect its soft abdomen and changes shells as it grows.

It is known as one of the most docile hermit crabs; it is less often seen attacking snails and other crabs. For this reason it is often preferred over the blue-legged hermit crab in reef aquariums. Specimens in the trade are wild-collected.

It lives on Caribbean coral reefs, among rock and coral rubble, in calmer and usually deeper areas than the blue-legged hermit crab. In the wild it cleans the fine algal film and organic debris from coral reefs.

• Volume: 40 liters or more; as a cleanup crew, 1 crab per 20–40 liters.
• Water: salinity 1.023–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C. Calcium and alkalinity should be kept stable.
• Reef compatibility: Reef-safe. It leaves corals alone; it may only knock over loose coral frags while roaming the rocks.
• Spare shells: keep 2–3 empty shells with slightly wider openings for each crab; a shortage of shells can turn even the most docile crab against snails.
• Acclimation and medication: Acclimate by the drip method for at least 1 hour. Copper-based medications are lethal.

Omnivorous. It feeds on hair algae, algal film on the rocks, detritus and leftover food; it is a good helper against hair algae. When algae run short, supplement with sinking granules, algae wafers or pieces of dried seaweed (nori); hungry crabs become more restless.

Calm and active during the day as well. It constantly combs the rock surfaces and sand. It gets along with its own kind; there may be brief shoving matches over shells, but serious fights are rare.

Good companions: clownfish, gobies, blennies, cardinalfish; cleaner, fire and peppermint shrimp, snails, emerald crab.

Avoid: triggerfish, pufferfish, large wrasses and lionfish; boxer shrimp.

It has no social needs; the number is determined by the amount of algae and debris in the aquarium. One crab per 20–40 liters is a general guideline. In the cleanup crew, snails should outnumber crabs. If different hermit crab species are kept together, the number of spare shells should be increased.

The female carries her eggs attached to her abdomen inside the shell. The larvae develop in the plankton and do not survive in home aquariums; it does not reproduce in the aquarium.

• Shell swapping: the crab may stay out of its shell for a short time; it is vulnerable during this period.
• Molting: a discarded molt that you find is not a sign of death.
• Sudden deaths: copper, rapid acclimation, sudden salinity changes.
• A crab that leaves its shell completely and does not go back in is usually under severe stress; the water parameters should be checked.

Practically impossible to tell apart externally. A cluster of eggs may be visible on the abdomen of a female out of her shell.