70 ANIMAL LIFE IN DESERTS 



of insects, in fact each species, finds this or that 

 month favourable to it for a different reason. The 

 mantises may be influenced by an abundance of 

 other insects on which they prey. The bees or 

 wasps may, for all we know to the contrary, time 

 their emergence more by the flowering season of 

 certain plants than directly by any cUmatological 

 event. The moths may fly at midsummer, not 

 because midsummer conditions suit them particu- 

 larly, but because several months before there was 

 abundance of herbage for their larvae. In fact, 

 Figs. 28 to 30 represent facts which are the result 

 of the action of very many factors : they cannot be 

 used as a basis of a theory. If we wish to interpret 

 the abundance of insects in a certain month, we 

 must take individual species of insects and study 

 their reactions to altered temperature, humidity, 

 food, soil, moisture, etc. We are not justified in 

 taking such curves as Figs. 28 to 30 and comparing 

 them without further analysis with the meteoro- 

 logical statistics, or the season of greatest plant 

 growth. 



In the British Isles we are accustomed to think 

 that the warmer the temperature to which insects 

 are exposed, the more quickly do they go through 

 the various stages of their Hfe-history. This is 

 clearly a fallacy, because in Mesopotamia in many 

 different families of insects active life is in abeyance 

 during the hottest months. We can at present only 

 guess at the cause ; it is probable that heat and 

 humidity interact in such a way that neither factor 

 can be considered separately : a certain high 



