Signal Crayfish

Fascinating facts about the Signal Crayfish

• Signal crayfish spread to 27 European countries by 2009, making them the continent's most widespread invasive freshwater crayfish. Introduced first in 1960, they now occupy waters from Finland to Greece, outcompeting native species and carrying the deadly crayfish plague that has decimated Europe's noble crayfish populations.
• During a 12-hour light-dark cycle, signal crayfish spend 72% of their activity at night, with early-night bouts predictable and late-night actions erratic. This nocturnal rhythm likely helps them avoid predators while exploiting food resources, giving them an edge over less flexible native crustaceans.
• Signal crayfish escape roughly 75% of their native parasites and predators when they colonize new waters, a phenomenon called the Enemy Release Hypothesis. Fewer enemies boost their survival and reproduction, explaining their rapid expansion and the difficulty of controlling their populations.
• When exposed to haemolymph, the alarm fluid of injured crayfish, signal crayfish increase swimming speed and linger near the source longer than they do for food cues. This heightened vigilance lets them gather information on threats while staying safe, illustrating a sophisticated risk-assessment strategy.
• Signal crayfish can reach 20 cm length. Adults typically weigh 60 g at 50 mm carapace length and 110 g at 70 mm.

Sources

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

• Wikipedia

At a glance

About the Signal Crayfish

In the crystal clear waters of North America's rivers and streams, the signal crayfish glides with stealthy precision, its vibrant blue-green shell glistening like a shard of stained glass as it navigates the submerged landscape. With a delicate touch, it probes the rocky crevices and weed-draped shallows, its antennae twitching with an almost imperceptible sensitivity as it searches for the tender shoots and decaying leaves that sustain it. As it moves, the signal crayfish leaves behind a trail of subtle disturbance, a whispered promise of life and renewal in the hidden world beneath the surface.

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