TankBud

Electric blue hermit crab

Calcinus elegans

Also known as Electric Blue Leg Hermit Crab, Blue-Banded Hermit Crab, Elegant Hermit Crab, Blue knuckle hermit crab

SaltwaterCrab

Electric blue hermit crab (Calcinus elegans)
Fafner · CC BY-SA 3.0

Care at a glance

Temperature
72–79°F
22–26°C
pH
8.1–8.4
Adult size
2 in
5 cm
Minimum tank
20 gal
75 L
Temperament
Peaceful
Social behavior
Solitary
Swim level
Bottom
Difficulty
Easy
Breeding
No record
Rarity
Common
Reef safe
Reef safe
Family
Diogenidae
Origin
Indo-Pacific, from East Africa to Hawaii and French Polynesia, north to southern Japan and south to northern Australia

Overview

An active scavenger that grazes green hair algae and cyanobacteria and cleans up detritus and leftover food, making it a genuinely useful cleanup-crew animal. It is generally peaceful toward fish and corals, so it counts as reef-safe, but it is not snail-safe: if it outgrows its current shell and no spares are available, it will attack and kill a snail to take its shell. Keep a good supply of empty shells in a range of sizes, and expect some squabbling over shells if several are kept together in a small tank.

In the wild

Ranges across the Indo-Pacific from East Africa to Hawaii and French Polynesia, north to southern Japan and south to northern Australia, living intertidally and on shallow coral reef and rubble down to about 5 metres. It grazes rock and rubble for algae and organic debris, carrying its shell home wherever it forages. In the aquarium it wants live rock with algae growth to pick at and enough open rock and sand to move around freely.

Good to know

Calcinus elegans is a hermit crab in the family Diogenidae, unmistakable for its electric blue legs banded in black and yellow, blue eyestalks, and green claws tipped in white. Adults reach about 5 cm in body length and grow into shells up to 7.5 cm long. Like other Calcinus it is a left-handed hermit: its left claw is enlarged and works as a door that seals the shell opening when it withdraws inside.

Did you know

Its enlarged left claw works as both a weapon and a trapdoor, folding flush across the shell opening to seal the crab safely inside whenever a predator gets too close.

Common questions

What size tank does an Electric blue hermit crab need?

An Electric blue hermit crab needs at least 20 gal (75 L). It spends most of its time in the bottom.

What temperature and pH does an Electric blue hermit crab need?

An Electric blue hermit crab is comfortable at 72–79°F (22–26°C) with a pH of 8.1–8.4.

How big does an Electric blue hermit crab get?

An adult Electric blue hermit crab reaches about 2 in (5 cm).

Related species