Sunday, 6 April 2014

More life under stones

Going around turning over logs and stones can be very revealing (if you can do it before the men in white coats arrive to whisk you away) with various cryptic animals to be found. Many of these creatures seem to be nocturnal, emerging from their lair to browse (slugs, etc) or to hunt (many carabid beetles). Woodlice also tend to emerge in cool, damp conditions after sunset. They are crustaceans, i.e. related to prawns, and, unless they have the ability to roll up into a ball (Armadillidium vulgare is the common "roly-poly") they could die from dessication. 

Platyarthrus hoffmannseggi revealed in my garden in
the "nest" of Lasius niger. 17 March, 2014
By far the commonest woodlouse under logs is Porcellio scaber, a rough-backed, dull grey animal (although pinkish forms are frequent) but if, when turning over a stone, you reveal an ants' nest, have a look for the myrmecophilous woodlouse Platyarthrus hoffmannseggi. Not only is it without eyes but it is albino, with neither sight nor pigmentation being required for a permanently subterranean existence. It is common throughout Northamptonshire and it occurs in my garden with the even commoner ant Lasius niger. It appears to be a scavenger in the nest, feeding on ant faeces. It is perhaps because it performs a useful function that ants accept its presence

Oniscus asellus is extremely common if marginally less so than Porcellio scaber, and tends to be a little larger. The exoskeleton of a woodlouse is impregnated with calcium salts and so in general they are commoner on limy soils, but Oniscus asellus seems able to tolerate acid conditions better than most.

Oniscus asellus in my back garden
29 March, 2014

Glossy, with pale edges to the sternites, Oniscus asellus is distinctive.

Tachypodoiulus niger  Found under a log at Calves Close
Spinney, near Chipping Warden. 13 March 2013

Some 45 species of millipede are found in Britain, with the majority generally occurring beneath stones or logs. The most familiar are the Julids, and the picture shows a typical and very common species, Tachypodoiulus niger.

Slugs are much-maligned creatures - and understandably so if you are a gardener. In fact, with over thirty species native to Britain, they deserve a blog to themselves. Many dwell beneath stones. The most infamous of all is the Common Garden Slug, Arion hortensis. The under-side of the animal (the sole) is orange in colour, as is the mucus. Also very common - and very distinctive - is the Leopard Slug, Limax maximus.

Leopard Slug at Steppington Spinney SP533568
3 April, 2014. The 

The Leopard Slug (the specimen shown has drawn its head in) is large, reaching 20 cms. The name is quite appropriate as it is usually distinctly spotted, although there are several colour varieties.

Creatures living under logs and stones - in fact animals in any habitat of this nature - are known as cryptozoans. The distribution and behaviour of many cryptozoans is poorly understood, making any observations useful. And always try to replace objects with as little disturbance as possible. 

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