Rollers, runners and creepers

I have always been fascinated by woodlice, shy creatures, some with an ability to roll into a ball if disturbed in their damp hiding places. They live quietly and do very little harm. So I was delighted to have an opportunity to learn about them from one of the leading experts on this species, Steve Gregory. He is a member of the British Myriapod and Isopod Group, amateurs and professionals with an interest in woodlice, millipedes and centipedes and related fauna.

Steve is leading a project to publish an updated atlas Woodlice in Britain and Ireland: Distribution and Habitat which last appeared in 1985 and as Oxfordshire is a good place to study them he is using the Northmoor Trust nature reserve at Little Wittenham as his base.

The BMIG is working closely on this with the Biological Records Centre at the Centre for Ecology and Hydrology, at present at Monks Wood, in Cambridgeshire.

Steve is also the organiser of the British and Irish Non-marine Isopod Recording Scheme. Interested in all aspects of wildlife from an early age, and an entymologist by profession, he says that he first began working on woodlice some 20 years agoin 1989 under the guidance of the late Steve Hopkin.

This new edition of the atlas is being produced because so much more information is available, in the same way that the first edition brought up to date an earlier work published in 1968.

"Twenty years later," said Steve, "we know so much more than we did in 1985. We understand a lot better how woodlice are distributed, and the effect of climate on distribution of populations and their ecology," said Steve. "There is so much new information that it seemed the time was ripe for another publication."

Woodlice are crustaceans, as are crabs and shrimps, but belong to the group Isopda, literally meaning equal feet.

The difference between the species - of which there are 39 in Britain and Ireland - is in some respect their means of self protection, said Steve. There are the rollers, those who curl up, the clingers, those who press themselves tightly into a stone, log or other home, relying on not being noticed, the 'runners', those who can move at speed, and the creepers, those who hide in the soil.

"Oxfordshire is a good place to study woodlice," says Steve. "It has a good overlap of south-western and south-eastern species and all the ones in between. But, unfortunately, it lacks coastline, where many scarce species live."

Those we see in our own gardens are mostly of the five most common species - the Famous Five, Steve calls them. They are abundant throughout southern England and are: The Common Pygmy Woodlouse (Trichoniscus pusillus), small in size, about five millimetres long, and purplish brown in colour; Striped Woodlouse (Philoscia muscorum) - this can run fast, having longer legs, and prefers grass, including lawns, as its habitat; Shiny Woodlouse (Oniscus asellus) commonly found in most places; Rough Woodlouse (Porcellio scaber), also found widely; Common Pill-Woodlouse (Armadillidium vulgare) - common in most places, and the species that curls up into a ball.

Distinctive, but common species that may also be seen in gardens are the Ant Woodlouse, (platyarthrus hoffmannseggii) - which lives only in ants' nests and is small and white, and the Rose Woodlouse, (Androniscus dentiger) one of the larger (up to six millimetres) of the 'pygmy' woodlice, which is bright orange in colour and usually living under large stones.

Secretive species, to be found on garden walls and rockeries, are two species which hide in crevices during the day but may be seen on the surfaces of walls at night - as may also the Shiny Woodlouse and Rough Woodlouse. One is the Southern Pill-Woodlouse (Armadillidium depressum), which although rare in Oxfordshire is numerous in the places where it is present; it is more flattened than the Common Pill Woodlouse and does not form a perfect sphere when it is rolled up. The other is the Painted Woodlouse (Porcellio spinicornus) which is common in the county.

"Churchyards are very good place to search for and study both common and scarce woodlice," said Steve, who has also published an Oxfordshire Distribution Atlas. Other types of habitat are associated with animals - and their manure, and therefore to be foundstables and dairy farms - and manure heaps.

Oxfordshire's ancient woodland provides a good home for two which are very rare nationally but in this county are widespread. The Carr Slater (Ligidium Hypnorum) likes waterlogged sites and is more common, but the Southern Ridgeback (Haplophthalmus montivagus) and Swiss Red-eye (Trichoniscoides helveticus) were both discovered here for the first time, at Wytham Woods, near Oxford, in 1987 and 1990 respectively.

Riverside meadows, of which Oxfordshire can offer plenty beside the River Thames, have enabled the Rough Pygmy-Woodlouse (Trichoniscoides albidus) and Rathke's Woodlouse (Trachelipus Mathkii) to feel at home. But nationally, these are scarce, but the available habitat in the Thames Valley has made them common here.

Some are more easily seen than others, but more easily found as knowledge about them increases. The Upland Pill Woodlouse was once thought to be extremely rare and found only in upland acid woodland, but a better understanding of its habitat has resulted in the discovery of a few more sites.

"We thought it was very, very rare," says Steve, "but now we know it is just very rare."

"This is an example of the better information we have," he added. "Before we didn't know how to find them, but now we know that they like places providing rotten wood or trees."

Woodlice like, and need, damp conditions. As chiefly vegetarians, they will feed generally only on vegetation, but not usually on flowers, so they are not much in conflict with gardeners.

They prefer decaying plant material, lichen and algae.

"They are a key component in decomposition and nutrient recycling," said Steve. "They are important in respect of mull soil, the rich loam that is ideal for growing crops as also are earthworms and millipedes. So they actually do something useful, despite what people think."

They can also act as detectives. They are very tolerant of metal pollution in the soil, such as from lead or iron. Their presence indicates such pollution and is valuable knowledge when environmental assessments are being carried out.

They are fortunate in having few predators. "Not many other species feed on them," said Steve. "They are quite tough and not very pleasant tasting." Their one threat is from the two species of Woodlouse Spiders, which make them their staple diet. These are spiders with unusually strong jaws, essential to bite through the 'armour plating' of these small crustaceans.

When the woodlice moult, however, shedding this hard covering, they can, for a short time, be vulnerable and at risk from small animals, birds and beetles.

I shall look forward to learning more about these fascinating creatures when the book on which Steve and his fellow experts are working appears.

The publication is very much a team effort. "We have input from as many people as possible. Everybody's expertise is being built in," says Steve.