370 . ENTOMOLOGY 



and makes possible body temperature regulation and thus prevents 

 heat stroke and death in warm blooded animals. In a moist warm 

 atmosphere, death and heat stroke occur because of lack of evaporation 

 and lack of peripheral cooling in the case of warm blooded animals 

 even when the surrounding temperature is at or below the normal body 

 temperature, (c) Wind movement (which increases evaporation) 

 increases radiation of body heat and of heat due to insolation. It 

 increases evaporation and further cools the body, thus within certain 

 limits increasing the metabolism of warm blooded animals and de- 

 creasing it in cold blooded animals, (d) Decrease of pressure increases 

 evaporation and radiation both of which lower the temperature of 

 animal bodies and influence metabolism. 



"Conditions which withdraw water from organisms (evaporation 

 as influenced by various factors) influence irritability, activity and 

 length of life history. Thus Hennings found that low humidity in- 

 creased insect metabolism and Sanderson found that in dry air the 

 optimum temperature of the growth of insects was lower than in moist 

 air. Factors probably operate with reference to an optimum." 

 (Shelford.) 



Professor Headlee raised bean weevils, Bruchus obtectus, from the 

 eggs at a constant temperature of 80 F., but with various degrees of 

 atmospheric moisture, from less than i per cent, to approximately 100 

 per cent. The optimum relative humidity was found to lie between 

 80 and 89 per cent. At 89.7 and 100 fungi developed and greatly re- 

 duced the numbers of the insects. Comparatively few individuals 

 reached maturity in an atmospheric moisture of 25 per cent, and none 

 in one of less than i per cent. 



Burger, as reported by Shelford, studied the water relations of 

 the meal worm, Tenebrio molitor when kept in dry air and fed on bran 

 which had been dried at 105 C. He believed that the animals were in 

 essentially absolute dryness. Here they lived for weeks, but lost 

 weight. He found, however, that the per cent, of water in the animals 

 remained practically the same until after death and came to the conclu- 

 sion that the insect larvae could not use their food to produce water and 

 so the living substance itself was used. No doubt the food taken pro- 

 duced water but this was not sufficient in quantity. The most important 

 fact brought out was that the per cent, of water remained about the 

 same in spite of the extreme dryness and rapid loss of moisture. 



Reactions. Professor Shelford, who studied experimentally the 

 behavior of various animals under different rates of evaporation, found 



