CHAPTER IX 

 SOME ASPECTS OF ECOLOGY— continued 



Humidity, p. 228. Light, p. 235. Atmospheric Pressure, p. 237. 

 Air Currents, p. 238. Food. The General Subject, p. 239 ; Vitamins, 

 p. 243 ; Symbiotic Micro-organisms, p. 245. Climate. Geographical 

 Distribution, p. 251 ; Climate in Relation to Seasonal Prevalence, p. 257. 

 Literature, p. 259. 



Humidity 



The influence of humidity on insects has attracted a good deal 

 of attention in recent years. Before considering the effects of 

 humidity as an ecological factor it is necessary to refer briefly to 

 the subject of water balance and kindred problems in the insect 

 body which have a very definite bearing upon it. While the 

 water necessary for the maintenance of the insect organism is 

 derived in the main from the food, there is evidence that at least 

 some part of it may be obtained from other sources. The meal- 

 worm {Tenebrio molitor) appears to be one of the insects that is 

 known to be able to make use of water resulting from the oxidation 

 of its own reserve substances. According to Buxton (1930) this 

 insect is able to regulate the proportion of water and dry matter 

 in its body. This ratio, it was found, was constant in starved 

 insects kept at several relative humidities over a period of a 

 month at 23° C. Certain insects appear to be able to absorb 

 water from moist air. Here the best-known example is the meal- 

 worm. The actual mechanism by means of which this " hygro- 

 scopic property " functions is, however, unexplained. According 

 to Buxton (1930) meal-worms lose weight when kept at 80 per 

 cent, or lower relative humidity : but if kept at 90 per cent, 

 humidity and at a temperature of 23° C. or 30° C. they gain in 

 weight. The mean gain in weight, Buxton states, represents 

 water ; and during twenty-three days at 30° C. and 90 per cent, 

 relative humidity, from 57 to 65 per cent, of the total weight of 



228 



