dwelling arthropods. They have no waterproof waxy cuticle on their exoskeleton and are therefore more likely to suffer from desiccation compared with other arthropods such as insects which have a well developed waxy layer. These animals excrete their nitrogenous waste as gaseous ammonia directly through their exoskeleton (rather than as urea or uric acid), this means that their exoskeleton needs to be permeable to ammonia and is therefore also permeable to water vapour. Gas exchange occurs in the 1st pair of anterior pleopods. These pleopods contain a pseudotrachea (a branching system of tubes) covered with a thin film of moisture to allow gas exchange over a relatively large surface area. This moist surface will also allow evaporation of water which will transpire out of the pleopods through a pore like opening. The fact that woodlice prefer high humidity and cooler temperatures is a direct consequence of the permeability of their exoskeleton to water and the loss af water from their respiratory pleopods. These preferences are behavioural adaptations to help reduce desiccation. Woodlice are frequently found in clumps or groups. When parts of their bodies touch a surface, woodlice slow down and will eventually stop if enough of their body comes into contact with an object or another woodlouse (thigmokinetic response). This type of behaviour will cause clumping of woodlice as they come into contact with each other as they explore their habitat. ] ]