Freshwater Spider Crab Care Guide - Aquarium Setup, Diet & Breeding

The Freshwater Spider Crab, also known as the Thai micro crab, is one of the smallest freshwater crabs kept in aquariums. Its rounded body is pale brown to greyish and covered in fine hairs, while its extremely long, delicate legs give it a spidery appearance. Despite its crab-like shape, it is far too small and fragile to be considered a conventional scavenging crab.

Limnopilos naiyanetri is native to Thailand in Southeast Asia, particularly the Chao Phraya River basin and associated slow-moving freshwater habitats. It is found among submerged roots, aquatic plants and other dense structure in calm, richly vegetated water.

A group can be maintained in an established aquarium of at least 20 litres, with a footprint around 30 by 30 cm or larger; extra floor area is more useful than great height. Use gentle filtration with a protected intake, stable water quality and plenty of Java moss, fine-leaved plants, driftwood and smooth surfaces for grazing and climbing. A thin layer of sand or fine rounded gravel is suitable, and leaf litter can provide additional cover and microscopic food. Avoid strong currents, sharp decorations and newly set-up tanks with little natural biofilm.

Adults reach about 1.5 cm (0.6 in) across the body, with a total leg span of roughly 2.5–3 cm (1.0–1.2 in). Females are usually slightly larger and more robust than males.

Freshwater Spider Crabs are opportunistic omnivores and filter feeders that browse biofilm, microorganisms, algae particles and fine organic matter from plants and surfaces. Offer mature aquarium surfaces, driftwood, moss and leaf litter alongside tiny amounts of powdered invertebrate food, spirulina powder or finely crushed sinking foods. Feed sparingly, as uneaten food can quickly pollute a small aquarium.

These shy crabs are best kept with peaceful nano invertebrates such as Neocaridina shrimp, small Caridina shrimp and carefully chosen freshwater snails. They can sometimes live alongside very small, non-predatory fish, but even peaceful fish may eat the crabs or compete with them for microscopic food. Avoid bettas, larger tetras, cichlids, gouramis, loaches, crayfish and any fish known to hunt small invertebrates.

Breeding Freshwater Spider Crabs in captivity is possible but uncommon and not yet supported by a dependable, widely established method. Females carry small clutches of eggs beneath the abdomen, and the young appear as minute crab-like juveniles rather than passing through a conspicuous marine larval stage. A mature, species-focused aquarium with abundant moss, biofilm and fine natural foods gives the best chance of success. Remove or separate fish and other predators, and avoid strong filtration intakes that can trap the tiny offspring.

Females generally have a broader, rounder abdomen and a fuller body, especially when carrying eggs. Males are typically slimmer, with a narrower abdomen and a more delicate appearance.