Signal Crayfish

Fascinating facts about the Signal Crayfish

• A signal crayfish can regrow a lost limb in as few as 5 moults — complete with working muscles, nerves, and claws. The new appendage starts as a tiny bud under the old shell and unfolds like origami when the crayfish sheds. Within two years, it's virtually indistinguishable from the original, though slightly smaller. This regeneration happens because crayfish retain juvenile stem cells throughout life, a trick most animals lose after development.
• Signal crayfish taste with their feet. Chemoreceptor hairs on their walking legs detect food dissolved in water from up to 2 metres away — the equivalent of smelling a drop of vanilla in an Olympic swimming pool. They follow scent trails by comparing signals between left and right legs, turning toward whichever side tastes stronger. This is how they navigate pitch-black stream bottoms at night.
• A female signal crayfish glues her eggs to her swimmerets — the swimming legs under her tail — and carries 200 to 300 babies for 4 to 8 weeks. She fans her tail constantly to keep water moving over them, protecting them from fungus and starvation. Newborns cling to her body for days after hatching, riding her like a living ark. If she dies, every egg dies with her.
• Signal crayfish have blue blood. Their copper-based oxygen carrier, hemocyanin, turns their blood bright blue instead of the iron-red blood of vertebrates. This molecule works better in cold water and low-oxygen environments, which is why crayfish thrive in streams where fish would suffocate. They can also extract oxygen from air for short periods, letting them survive out of water for several days if it stays damp.
• Native to Pacific Northwest streams, signal crayfish were exported to Europe in the 1950s as food and aquaculture stock, then escaped into wild waterways across Scandinavia, Britain, and France. They carry a waterborne plague fungus harmless to themselves but lethal to native European crayfish species — populations have collapsed by 99% in some regions. Signal crayfish are now considered one of Europe's most destructive invasive species, a cautionary tale of how one continent's dinner becomes another's ecological crisis.

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.

Discover more wildlife