94 A BIOLOGY OF CRUSTACEA 



istic display and coloration indicate to a female the presence, in a 

 breeding condition, of a male of her own species. 



There is a great multiplicity of activities in which Crustacea 

 indulge, but we cannot deal with them all here. Many are men- 

 tioned in the writings of the great naturalists, particularly Darwin. 

 In general we can say that these activities are directed towards the 

 crustacean's own well-being: they have their special escape move- 

 ments, such as the violent flexing of the abdomen in the crayfish, 

 or the rapid darting of Cyclops — a most successful procedure, as 

 anyone who has tried to catch these copepods with a pipette will 

 know. They have maintenance activities, such as burrowing, clean- 

 ing their limbs, and feeding; these activities are diversified and 

 adapted to the particular set of conditions in which a species 

 lives. 



It is not much use an animal being adapted to live in a particular 

 set of conditions if it does not behave in such a way as to keep it 

 in those conditions. From this point of view the behaviour of an 

 animal is one of the most important features of its relationship 

 with its environment. The Crustacea provide a wide range of com- 

 plexity of behaviour, and examples can be chosen to show how the 

 behaviour of a species is related to its survival and to the particular 

 set of conditions in which it is best suited to live. The woodlice are 

 probably the best of these examples. 



Woodlice live in damp places, and have a remarkably simple 

 behavioural mechanism for keeping them in such places. They tend 

 to stay still more often in damp situations than in dry ones, and 

 they walk more quickly in dry places than in damp ones. This 

 means that as soon as a woodlouse enters a dry area it begins to 

 walk more quickly, but when a damp area is found the woodlouse 

 may stop, or at least walk more slowly. Clearly in this way they will 

 aggregate in damp places. No directional response is needed, it is 

 merely a matter of increased locomotory activity in dry conditions. 

 This simple mechanism is a life saver, because a woodlouse, such as 

 Porcellio, dies in about six hours in dry air. 



There are, of course, other factors in the life of a woodlouse. The 

 normal reaction to light is for the woodlouse to move away from it; 

 this tends to lead it to dark, damp places. But what if the dark 

 place becomes dry, can the woodlouse overcome its negative re- 

 action towards the light and move out before it dies of desiccation? 

 In fact, a woodlouse becomes attracted towards the light when 

 suffering from desiccation. This, at first sight, seems suicidal, but 



