CHAPTER VI 



THEIR RELATION TO WEATHER AND DISEASES 

 THAT AFFECT THEM 



Very few insects occur throughout the world, and 

 those that do are usuall" such as have been distributed 

 by or have followed in the track of man or his commerce ; 

 but there is no portion of our globe where life occurs 

 at all, in which insects are not found. In the polar 

 regions they are often unpleasantly conspicuous, and 

 in the tropics they frequently render life burdensome. 

 When the arctic snows begin to melt during the short 

 summer and form puddles on the mossy surface, mos- 

 quito larvae appear, and even when there is an ice coat- 

 ing over the pools at times they maintain themselves 

 and come to maturity. Indeed some wrigglers and other 

 insects will stand freezing or imbedding in ice, and come 

 out none the worse when a warmer temperature thaws 

 them into a liquid medium. There are insects, then, 

 that survive in one condition or another the extremes 

 of arctic cold: there are others that flourish under the 

 opposite conditions of tropical heat. Indeed the lux- 

 uriant vegetation of the equatorial regions is accom- 

 panied by an infinite variety of insect life, a variety so 

 great that we have just begun to appreciate it, and 

 which will give a field for study to entomologists for 

 generations to come. Furthermore, as we have found 

 aquatic forms in water at temperatures low enough to 

 form ice, so we find others in waters whose temperature 

 ranges close to the boiling point. There are some 

 regions so arid that neither vegetable nor animal life 

 exists in them; but if at any time under the influence 

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