The revenge of nature

Little walk along the creek this morning. Two red spots in the water. This should be a dead crayfish.

Indeed this is a signal crayfish, (Pacifastacus leniusculus), the North American species of crayfish, which is currently invading European water bodies. This species is easy to recognize with a white to pale blue-green patch near the claw hinge.

 

It may have been killed by “our” heron (see post “flying fish” dated 10/12/2015, on Fauna & Flora page) which escaped when I arrived with my dogs.

The history of the invasion of signal crayfish is a good example of men ignorance of risks when playing with Nature. From 1907, crayfish plague, an infectious disease caused by the water mould, damaged stocks of the native European crayfish. Since the signal crayfish occupied a similar ecological niche in its native range, it was imported in the 1960s to Sweden and Finland to allow recreational and commercial crayfish capture. It was not realised at the time that the signal crayfish was a carrier of the crayfish plague. All American species carry the infection, but it is only lethal to individuals that are already stressed; to European species, the infection is rapidly fatal. The signal crayfish is now the most widespread alien crayfish in Europe, occurring in 25 countries, from Finland to Great Britain and from Spain to Greece.