4 WOODLICE 



abundant in deciduous woodlands than elsewhere, while P. detni- 

 virgo definitely prefers moist woodland situations. 



With regard to the British species, Heeley (1941) notes that 

 Trichoniscus pusillus is abundant in very moist woodlands, though 

 the animals are frequently overlooked owing to their small size and 

 dark colouring. They can easily be mistaken for young Philoscia. 

 They favour the thick sodden layers of decaying leaves which lie 

 beneath the trees throughout the winter and during the summer 

 they live amongst the resulting leaf mould beneath low bushes 

 well shaded from the sun, or within rotting twigs. 



Philoscia muscorum is fairly common in moist shady situations 

 in moors and woodlands, particularly amongst the roots of grasses 

 beneath bushes and brambles and at the base of tree trunks, where 

 the soil receives the drippings from the trees and is shaded from 

 the sun. This species is somewhat local and restricted in its dis- 

 tribution and is present mainly in woodland. Onisciis asellus on the 

 other hand is the commonest of all woodlice and is found almost 

 everywhere that damp conditions prevail, particularly beneath 

 half buried stones and bark. It seems to prefer rather more moist 

 situations than Porcellio scaber and may often be found with the 

 latter in the same tree, but usually nearer the ground where the 

 wood is old and rotting. 



Porcellio scaber is also very common, particularly beneath the 

 dry loose bark of vertical trunks of living trees. It sometimes in- 

 habits damp houses and has been found in heaps of clinker and 

 the nests of wood ants, Formica rufa. 



Finally, Armadillidium vulgare is particularly common on chalk 

 lands, on heaths and slopes covered with low scrub such as are 

 found in railway cuttings and on roadsides. The species also oc- 

 curs in the neighbourhood of houses and builders' yards where 

 there is loose cement or lime, but is never very numerous in wood- 

 land. It can even survive under dry stones warmed by the sun. 



Now Heeley claims that it is possible to predict which species of 

 woodlouse will be present in a given habitat by its water-content. 

 In his experiments, however, he provided a moist surface for the 

 animals in the form of a carrot as food. It has since been shown 

 that woodlice of the same species, if desiccated and subsequently 

 kept in unsaturated air, but with access to moist plaster of Paris 



