Nature Notes

Jenny Dixon

Wharfedale Naturalists Society

A LIFE-long interest in Natural History has led me, not surprisingly, to accumulate a large library – field guides, memoirs, studies of individual species and autobiographical accounts of encounters with wildlife and life in the wild. I keep intending to cull the collection but lack the energy and, of course, the will! Those volumes in constant use tend to be the field guides to everything from wild flowers to spiders, from bumblebees to birds. One book I could never part with is a battered copy of Collins Guide to Animal Tracks and Signs. A walk through fields and woods apparently devoid of wildlife has often been saved by finding a fox scat placed artfully on a tussock of wayside grass, a pinecone which, my Guide tells me, has been fed on by a crossbill, or the still-slightly-warm form in the grass newly vacated by an unseen hare.

My friend Gary was peacefully fishing on the Wharfe on a recent sunny evening when his eye was caught by just such a trophy. On the bank nearby lay a large orangey-brown double claw. Not far away he found its partner. He recognized them as the pincers from a signal crayfish, a kind of freshwater lobster, and this one must have been a whopper. The signal crayfish is an alien species from America, brought to the UK to be farmed. Though they live in water, crayfish can travel overland for considerable distances in rainy weather, they just need to keep wet. It wasn’t long before they escaped from fish farms and, alas, quickly spread throughout most of the Dales river systems, outcompeting the much smaller native British crayfish and infecting them with crayfish plague. There are still a few streams left where the latter survive and attempts are now being made to preserve them, but it’s a story very like that of the grey squirrel – hard to bring to a happy ending.

What was particularly interesting about Gary’s find is that along the edges where the claws had been attached were the marks of sharp teeth. The claws had been neatly sheared off by an otter. There are lots of signal crayfish in the Wharfe: the otter population on our river seems to be doing well. A connection here, perhaps? The following week at the same place there were further crayfish remains – this time many large fragments of the plate-like armour in which the creature is encased. Seems like a good news story.