TIME AND ANIMAL COMMUNITIES 95 



conditions only, and is more or less unaffected by the light or 

 darkness. 



18. The effect of weather upon the habits of animals has 

 a certain practical importance, since weather conditions control 

 the habits of many blood-sucking flies, and their disposition 

 to bite people. The tsetse fly {Glossina palpalis), which 

 conveys sleeping sickness to man by its bites, is entirely a 

 diurnal feeder, but also shows a marked tendency to bite more 

 on some days than on others. Carpenter *^ says : *' The time 

 when they are most eager to feed is early in a morning after 

 a little rain, when the sun is hardly through the clouds, and it 

 is close and still," while, on the other hand, '* if one wishes 

 to avoid being bitten [the time] is in the middle of a day 

 on which there is a fresh breeze, cloudless sky, and brilliant 

 sun." 



19. Seasons of the Year. — It is unnecessary to say very 

 much about this subject since, although its importance in 

 ecology is immense, the general facts of annual changes and 

 their effects upon the fauna are so well known as to require no 

 underlining. In temperate regions the annual changes in 

 plants and animals are primarily caused by variations in the 

 amount of heat and light received from the sun. In sub- 

 tropical countries this is also true, but there are often in addition 

 very big variations in the rainfall, which are much more 

 abrupt and regular than in more temperate climates. In the 

 actual equatorial belt, with rain-forest, the temperature may 

 be practically the same all the year round, while rain may be the 

 only important climatic factor in which there are marked 

 annual changes. In the Arctic regions the winter is so cold 

 that active life among land animals (other than warm-blooded 

 ones) is confined to the short summer season. It seems 

 probable, then, that the greatest richness in variety of com- 

 munities found at different times of year is in the temperate 

 and subtropical regions, although the actual profusion of species 

 is not so great as in the tropics. 



20. The difference between winter and summer in a country 

 hke England is sufficiently great to change the animal com- 

 munities to a considerable extent. This is a matter of every- 



