94 ANIMAL ECOLOGY 



because it wets their fur, and, by destroying the layer of warm 

 air round their bodies, upsets their temperature regulation 

 and makes them liable to catch cold. Mice tend to stay at 

 home when it is raining hard, and the badger has to he in the 

 sun to dry himself if he happens to get wet. Birds are not 

 quite so much affected by weather conditions, since the 

 architecture and arrangement of their feathers usually act as 

 a more efficient run-off for rain. Many insects also necessarily 

 stop work during wet weather owing to the danger of getting 

 their wings wet, or to the drop in temperature often associated 

 with the rain. 



1 6. There are, on the other hand, certain animals which 

 come out only when it is wet (either when is is raining or when 

 the ground is damp after rain). Slugs form a good example 

 of this class of animal. This rule does not apply to all slugs, 

 for there are some species which always Hve in damp places, 

 as under vegetation ; it holds good mainly for certain of the 

 larger wide-ranging slugs. A record of the activity of slugs 

 was kept for some weeks in woods near Oxford, when the 

 writer was trapping mice. The slugs visited the traps for the 

 bait, and every morning the number of slugs was counted. 

 The number of slugs walking abroad fluctuated greatly, and 

 appeared to be determined mainly by the rain or dampness of 

 the ground. These results were confirmed by casual observa- 

 tions on the general occurrence of slugs on different days. 

 On some days slugs might be seen practically waiting in queues 

 trying to get into the mouse- traps, while on other days the 

 latter would be entirely deserted. 



17. These examples serve to illustrate the general idea that 

 animal communities vary according to the weather conditions, 

 and that the variations follow a comparatively regular sequence, 

 although the actual times and periods of the cycle are irregular. 

 We have, broadly speaking, communities of fine weather, of 

 wet weather, and of drying-up weather, but they grade into 

 one another to a large extent. One significant thing is that 

 the weather-cycle may entirely override that of day and night, 

 as in the case of certain slugs. One big black slug with a grey 

 stripe down its back {Limax cinereo-niger) comes out in wet 



