October 2011 Archives
Life is not easy for white-clawed crayfish. Once found almost everywhere in suitable waters in England and Wales this miniature cousin to the lobster is declining everywhere.
Overall its numbers are down by between 50% and 80% compared to 20 or 30 years ago, and in some places it has become extinct or has been reduced to a few small and isolated populations.
The Midlands remain one of its strongholds but the species which, outside Britain and Ireland, is only found in north-west Europe (from the Balkans to Spain) is endangered everywhere.
Slow-moving and unobtrusive white-clawed crayfish are up to 12 cms long, olive-green or brown and look just like little lobsters complete with big claws.
They need clean calcareous water with places to hide such as overhanging banks, tree roots and rocks. They are mainly nocturnal and will eat plants, animals, or detritus, and can live for ten years or more.
Apart from the usual problems for freshwater wildlife, such as pollution, engineered changes to streams and rivers and the clearance of bank side plants, this, our only native crayfish, suffers from competition from an introduced species - the American signal crayfish - and a deadly fungal disease which the interloper carries.
Its situation almost exactly mirrors that of the red squirrel: in both case the native species is both smaller than its American relation, and is susceptible to a disease carried by, but not seriously affecting, the newcomer.
For this reason the Staffordshire Wildlife Trust is appealing for help following the discovery of the disease in the Sherbrook on Cannock Chase, where there is a good population of white-clawed crayfish.
The trust's senior wetlands ecologist, Nick Mott, said: "This is devastating news as Cannock Chase has always been a stronghold for our native crayfish. The disease can be transferred to them via a number of 'wet pathways' including direct contact, footwear, animal coats, fishing kit or pond nets."
To help prevent the disease spreading, people are being asked to avoid entering the Sherbrook for the next few months or until there is confirmation that the disease has died out.
Once confirmation has been received, stream users can help to stop it returning by removing all mud and plant matter from footwear, pond-dipping nets or anything that has come into contact with water, then washing in clean water at home and drying thoroughly or disinfecting it before using it again in another pond or stream.
Dog owners and horse riders can also help by keeping their animals out of the water.
These precautions could usefully be applied whenever and wherever people have been in and around rivers, streams and ponds. The more protection we can give our native crayfish the better.
If you want to know more a booklet about freshwater crayfish is available free from the Trust: call 01889 880100, or download a copy from http://www.staffs-wildlife.org.uk/page/white-clawed-crayfish.
Autumn is the prime time for a very common and numerous, but little known, group of spider-like animals called harvestmen. In Britain there are about two dozen species of these otherwise mainly tropical creatures of which there may be 10,000 species worldwide. They are close cousins to spiders (with several hundred species in Britain) for which they are often mistaken. Harvestmen though lack the poison glands and silk-making ability of spiders, and are probably more closely related to mites and scorpions. The average garden or park will probably be home to nine or ten species, a higher than average proportion of the total number of species in this country when compared to other groups.
Harvestmen are remarkable creatures. Like spiders they have eight legs and in many species these are very long and thin, perhaps the longest legs in relation to their bodies of any other animals. The second pair is always the longest and act as sensory organs as well as being used for walking. They seem to perform the same functions as antennae do in insects, with harvestmen constantly waving them and using them to probe the ground ahead. Their small and round one-piece bodies are suspended above the ground by the legs, and are often topped by a turret-like appendage called an ocularium. This carries two outward facing eyes. Here is another difference to spiders, which have six or eight eyes. Overall many harvestmen look like miniature monsters from science fiction.
Those long thin legs are easily and frequently lost, but they do not regrow. When a harvestman loses one whilst being attacked by a predator the detached leg continues to move and jerk about, thus acting as a decoy whilst the harvestman limps away.
Harvestmen are nocturnal hunters and scavengers. They eat almost any animal and vegetable matter, alive or dead, including bird droppings. During the day they rest in leaf litter, grass and other plants or on trees and walls. They prefer shady places, so may be found beneath window sills or in deep cracks in bark. When disturbed they move surprisingly quickly considering their ungainly appearance.
The name 'harvestman' arises from the huge numbers of these creatures found at this time of the year. Because of their habit of sheltering in grasses and other plants many of them were disturbed during hay-making and harvesting. They are also sometimes referred to as 'daddy-long-legs', although that epithet really belongs to crane flies, which are also prominent in late summer and autumn. If you disturb a 'spider' whilst gardening at this time of the year take a closer look - the chances are you have roused a sleepy harvestman.