Woodlice
Introduction
Woodlice, are often found in the upper layers of compost heaps, under rotting wood or logs, under
surfaces or stones, and in other dark, damp places. Woodlice belong to the biological class Crustacea.
Most of the animals in this class are aquatic, and although the terrestrial species can breath with the
aid of primitive "lungs," they lack the features found in most other land dwelling arthropods. They do
not have a waterproof waxy cuticle on their exoskeleton, like insects, and are therefore more likely to
suffer from desiccation. Woodlice excrete their nitrogenous waste, ammonia gas, directly through
their exoskeleton. This means that the exoskeleton needs to be permeable to ammonia and is therefore
also permeable to water vapour. The fact that woodlice prefer high humidity and cooler temperatures
is a direct caused by the permeability of their exoskeleton to water; these preferences are behavioural
adaptations to help reduce desiccation.
Orientattion Behaviour:
Kinesis: A non directional response of the whole organism to a stimulus e.g. Temperature or
humidity;
As the intensity of the stimulus changes the rate of turning or the speed of movement may change
Taxis: A directional response to a stimulus e.g. light; movement towards the stimulus is a positive
taxis movement away a negative taxis.
Many of the behavioural responses of woodlice are concerned with water conservation and the need to
avoid desiccation. They have a relatively high surface area to volume ratio and are therefore likely to
loose water by diffusion more quickly than many other species. Porcellio scaber show a kinesis type
response to moisture. That is they show both an increased speed of movement, (orthokinesis), and
increased rate of turning, (klinokinesis), in dry conditions and slower rates of movement in more
damp conditions. This response will result in them accumulating in more damp regions, and so reduce
the amount of water lost from their bodies.
Woodlice also show a positive orthokinesis as the temperature increases or decreases from their
preferred range. Their rate of turning also seems to show a similar response. By moving more rapidly,
they are likely to spend less time in these unfavorable conditions and therefore will avoid unnecessary
desiccation.
Woodlice also show a negative phototaxis as well. This would result in them moving away from
bright conditions towards darker regions. Brighter conditions tend to be drier and warmer than dark
conditions, so this behavior will again result in decreased desiccation.
Finally, these animals have been shown to demonstrate positive thigmokinesis. This means they are
less active when more of their body surface is in contact with other objects, including other woodlice.
They will move around so that the maximum amount of their body is in contact with other objects.
This behavior results in woodlice forming groups or clumps and also means they will tend to
congregate in cracks and crevices. In any case, they will have better protection from desiccation and
also predators.
There are 37 known species of woodlice in the United Kingdom. Each of these species has a different
niche being adapted to a range of different abiotic and biotic factors. By specialising they avoid
interspecific competiton and increase their chances of surviving and reproducing.