INSECT ECOLOGY 369 



in other conditions of the atmosphere (Shelford), doubtless exerts 

 some influence on the activities of insects and other animals, but in 

 regard to this subject little is known. 



In the literature there are observations of the effects of electrical 

 storms on insects, but these effects are results of several influences 

 operating in combination (as temperature, moisture, pressure, light, 

 and wind and rain acting mechanically); and possible effects of elec- 

 tricity alone are not distinguishable. 



EVAPORATION 



Evaporation depends upon air-temperature, pressure, relative 

 humidity, air-movement and, indirectly, light. The amount of evapo- 

 ration expresses the total effect of these factors. The evaporating power 

 of the air is "by far the best index of physical conditions surrounding 

 animals wholly or partly exposed to the atmosphere. " (Shelford.) The 

 rate of evaporation is directly correlated with temperature and illu- 

 mination, but most closely correlated with relative humidity. (Yapp.) 



In the experimental study of evaporation Livingston's atmometer 

 is usually employed. This consists essentially of a cup of porous clay 

 which is filled with water, that is replaced as it evaporates, from a 

 reservoir of water. The amount of evaporation is easily measured by 

 the amount of water necessary to restore the water in the reservoir 

 to its original level. 



Few precise studies have been made upon the effects of evaporation 

 on insects, though many have been made with man and other warm- 

 blooded animals. 



Metabolism in Relation to Evaporation. "Metabolism results 

 in heat, and the temperatures of the bodies of animals both warm and 

 cold blooded, is nearly always higher than the surrounding medium, at 

 least during activity. The surrounding conditions may be stated as 

 usually acting on metabolism, etc., as follows: (a) A moist cold atmos- 

 phere (very low evaporation) causes body temperature to fall more 

 rapidly than a dry cold one at the same temperature, because of the more 

 rapid conduction of heat. Such a fall in temperature decreases metab- 

 olism of cold blooded animals, and increases metabolism of warm blooded 

 animals within their capacity for heat regulation. In a dry cold atmos- 

 phere the heat loss is less pronounced because of the less rapid conduc- 

 tion of heat, (b) In a dry warm atmosphere (high evaporation) rapid 

 evaporation keeps down the peripheral temperature, and prevents death 

 from over-heating and destructive metabolism in cold blooded animals, 



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