Red Mithrax Crab

Mithraculus forceps

Also known as Ruby Mithrax Crab, Red Clinging Crab, Ruby Clinging Crab, Red Ridged Clinging Crab

SaltwaterCrab

Red Mithrax Crab (Mithraculus forceps) — Pauline Walsh Jacobson · CC BY 4.0

Care at a glance

Temperature: 75–82°F (24–28°C)
pH: 8.0–8.4
Adult size: 2 in (5 cm)
Minimum tank: 11 gal (40 L)
Temperament: Mostly peaceful
Social behavior: Solitary
Swim level: Bottom
Difficulty: Easy
Breeding: Hard
Rarity: Common
Reef safe: Reef safe with caution
Origin: Western Atlantic and Caribbean, living in coral rubble and reef crevices from Florida to Brazil.
Family: Mithracidae

Overview

A single crab suits a tank of 40 litres or more at 24 to 28 C and pH 8.0 to 8.4. It scrapes hair algae, film algae, and some bubble algae off live rock and eats leftover food. A well fed crab is a useful cleaner, but a large or underfed one may start picking at coral polyps or bother small snails, so keep it fed and watch bigger individuals.

In the wild

The red mithrax is a small Caribbean clinging crab with a deep red to reddish brown carapace and blunt spoon-tipped claws. It spends the day wedged in rock crevices and comes out at night to graze. In the wild it lives on offshore reefs rather than the inshore rubble the green emerald crab prefers.

Good to know

Mithraculus forceps is a close relative of the emerald crab, Mithraculus sculptus, and reaches a similar span of about 5 cm across the legs. Its rounded claw tips are built for scraping algae off hard surfaces rather than tearing prey.

Did you know

It is one of the few crabs that will eat bubble algae, the round green Valonia that spreads across neglected rock, which is why reef keepers add it to nuisance algae cleanup crews.