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.
