American Signal Crayfish

Fascinating facts about the American Signal Crayfish

• Signal crayfish can grow to the size of a small hand-held flashlight, reaching up to 20 cm (8 in) long and weighing as much as 110 g when their carapace measures 70 mm. Most adults are 6-9 cm (2.4-3.5 in) and weigh about 60 g at a 50 mm carapace. Their smooth, brown-to-bright-red shells hide a pale flag-like patch near the claw hinge that gives the species its name.
• First shipped to California's San Lorenzo River in 1912, the signal crayfish has since leapt across continents, arriving in Europe in 1960 and now inhabiting 27 countries, the most widespread invasive freshwater crayfish in Europe as of 2009. Its deliberate releases to replace dying native noble crayfish unintentionally turned it into a carrier of the deadly crayfish plague, wiping out native species wherever it spreads. This massive range shows how a single human-driven introduction can reshape entire freshwater ecosystems.
• Signal crayfish are night-time specialists: in a controlled 12-hour light/dark cycle, 72 % of their activity occurs during darkness. Their circadian rhythm splits into consistent early-night and middle-night bouts, while late-night actions become erratic, likely to dodge predators.
• A fungal survey of Lithuanian crayfish found that every examined signal crayfish (100 % of the two individuals sampled) hosted fungi, matching the infection rate of the native noble crayfish. Across 27 crayfish, researchers isolated 77 fungal strains, with 81.5 % of infections in muscle tissue.
• When signal crayfish invade new waters they leave behind roughly three-quarters of their native parasites and predators, a phenomenon called the Enemy Release Hypothesis.

Sources

Every fact above was checked against these pages, and kept only where one of them states it.

• Wikipedia

At a glance

About the American Signal Crayfish

In the sun-dappled streams and rivers of North America, the American Signal Crayfish navigates its domain with deliberate, sideways grace, its vibrant blue claws snapping softly as it probes the shadows for unsuspecting morsels. With eyes that swivel independently, this diminutive crustacean surveys its surroundings with an air of quiet confidence, its very presence a testament to the intricate web of life that binds these freshwater ecosystems together. As it moves through the water, its signal flag - a vibrant blue spot on its claw - flashes like a tiny beacon, a striking advertisement of its identity in this hidden world.

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