Crabs

Freshwater crabs are some of the most rewarding invertebrates in the hobby and the most commonly killed by good intentions. Nearly every crab that dies in its first month dies for one of two reasons: it was put in a tank with no land when it needed land, or it climbed out of a tank with no lid. Get those two right and most of the rest is easy.

First question: aquatic or semi-terrestrial?

This is not a preference. It decides whether the animal lives.

Semi-terrestrial crabs — the whole Geosesarma group, which covers vampire crabs, red devils, mandarins and pandas, plus red apple crabs — breathe air. Kept fully submerged with no way out, they drown. They need a paludarium: a land area they can climb onto and stay dry on, humid air above it, and shallow water. Roughly half land to half water is a sensible starting point, with the land side planted, moss-covered and kept damp.

Fully aquatic crabs — Thai micro crabs, pom pom crabs, panther crabs — live underwater the way a fish does and go into a normal aquarium.

If you take nothing else from this page: do not buy a vampire crab for a standard aquarium.

Escape-proofing

Every crab on this page is an escape artist, including the aquatic ones. They climb silicone corners, filter intakes, airline tubing, heater cables and plant stems. A crab loose in a house is usually found days later, dried out, behind furniture. Use a tight-fitting lid, close the gaps around cords and intakes, and keep the waterline a few inches below the rim. This is not optional equipment.

The species we carry

Geosesarma vampire crabs (purple bogorensis, disco, mandarin, red devil, panda) are the showpieces — vivid purple, orange and cream, about an inch across, active in the open, and genuinely watchable. Unusually for crabs, they breed in pure freshwater: the females carry a small number of eggs that hatch as miniature crabs, with no marine larval stage. That makes a stable colony realistic in a home paludarium, which is not true of most crabs sold in the trade. Keep them warm and humid, give them far more hiding places than you think are needed, and expect the males to squabble over territory.

Thai micro crabs (Limnopilos naiyanetri) are the opposite in every way — fully aquatic, fingernail-sized, fuzzy, shy, entirely peaceful, and safe with shrimp and small fish. They spend most of their time clinging to moss and filter sponge picking at the current. Excellent in a planted nano, provided nothing in there is big enough to eat them.

Pom pom crabs are fully aquatic, small, and carry setae on their claws that look like little pompoms, which they wave while feeding. Peaceful, good community inverts.

Panther crabs (Parathelphusa, from Sulawesi) are fully aquatic and the largest here. They are also predatory — shrimp, snails and small slow fish are food. House them alone or with fish too large and fast to catch, and give them harder, warmer water than the average planted tank runs.

Molting

Crabs grow by shedding their shell, and the days around a molt are when they are vulnerable. Three rules: make sure there is calcium available in the water or the diet, because the new shell has to harden; provide dense cover so the crab can hide while it is soft; and leave the shed exoskeleton in the tank, because the crab will usually eat it to recover the minerals. A crab that has disappeared for a week has almost certainly gone off to molt, not died.

Feeding

All of these are omnivores and scavengers. A varied diet beats any single food — sinking pellets, algae wafers, bloodworm, and for the semi-terrestrial species, small amounts of fresh fruit and vegetable matter on the land side. Add a calcium source: cuttlebone, crushed coral in the substrate, or a mineral supplement.

Ask before you buy

Crab requirements vary more between species than almost any other group we sell, and the setup has to be right on day one rather than adjusted later. Tell us what tank you have and we will tell you which crabs on the list will work in it — and which one you should build a paludarium for instead. Both stores are happy to talk it through, and see invert supplements for calcium and mineral products.