Crayfish (e.g. Astacus astacus)

CrustaceanFreshwaterRecycler

Overview

Crayfish — also called crawfish, crawdads, or yabbies — are freshwater crustaceans that look like small lobsters, with a hard exoskeleton, a pair of large pincing claws, and several pairs of walking legs. The European crayfish (Astacus astacus), shown here, is one well-known species among hundreds worldwide. Closely related to true lobsters, crayfish live in rivers, streams, lakes, and ponds, where they hide among rocks and in burrows and come out to forage, mostly at night.

Crayfish are important members of freshwater ecosystems — both as recyclers and predators, and as prey for many other animals — and in clean habitats their presence can signal good water quality.

Note: “crayfish” covers many species on several continents; details here use the European crayfish as a reference. Treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Crayfish live in fresh water on most continents — in streams, rivers, lakes, ponds, and wetlands — wherever there is suitable cover and reasonably oxygenated water. Many dig burrows in banks or beds, and some can survive in seasonal waters by burrowing down to stay moist. They generally avoid strong light, sheltering by day and foraging at night.

Diet

Crayfish are omnivores and scavengers with broad appetites. They eat water plants, algae, insects and their larvae, worms, snails, small fish, and dead and decaying matter, helping recycle nutrients in their habitat. Their strong claws let them handle a wide range of food, from tearing plants to seizing small prey.

Behavior

Crayfish are mostly solitary and territorial, defending shelters and using their claws in disputes and displays as well as for feeding and defence. Like other crustaceans they grow by moulting — shedding the old exoskeleton and hardening a new, larger one — and they can regrow a lost claw or leg over successive moults. If startled, a crayfish can shoot backwards rapidly by flipping its muscular tail (the “tail-flip” escape). They are mainly nocturnal foragers, retreating to cover during the day.

Human Interaction & Conservation

Crayfish have a complicated relationship with people. They are widely caught and farmed for food, and many native species are valued — some are sensitive to pollution and act as indicators of clean water, and several are of conservation concern. At the same time, certain crayfish introduced outside their native range (such as the signal and red swamp crayfish) have become serious invaders, outcompeting natives, damaging banks by burrowing, and spreading disease, so they should never be released. Consult authoritative sources for species-specific status.

More photos of the crayfish