THE SOCIAL INSECTS 



In vertebrates, there is a rough correlation between the size 

 of the brain and the mental powers of the animal. Because 

 insects are so small, their brain is minute compared with that 

 of a mammal and on analogy one would not expect it to be 

 very efficient. One certainly would not expect it to be 

 capable of producing intelligent behaviour. It is probable 

 that owing to great differences in plan the analogy is a false 

 one. The behaviour of such insects as the honey bee shows 

 that the insect brain must be a remarkable structure in spite 

 of its small size. 



Insects are " cold-blooded " animals. This does not mean 

 that they cannot raise their own temperatures, but only that 

 they have no mechanism for maintaining them constant, 

 particularly at levels above their surroundings. When flying 

 or otherwise very active they produce a considerable amount 

 of heat and may raise their temperatures several degrees, but 

 this excess is soon lost when the activity ceases. It is, of 

 course, physically much more difficult for a small body to 

 remain at a different temperature from its surroundings than 

 it is for a larger one. Scales or hairs may partly hinder the 

 loss of heat but they are not very efficient in small insects. 

 Actually, as will be seen later, most social insects are able to 

 maintain their nests at quite a high and often fairly constant 

 temperature. This is due to the contributions of a large 

 number of separate individuals as well as to the structure of 

 the nest which is usually such as to prevent the flow of heat. 

 Apart, however, from such special cases, insects tend to do 

 everything, including movement, feeding, and development, 

 at a speed which is related to the temperature of their sur- 

 roundings. Shapley, the American astronomer, measured the 

 speed at which ants travelled along their runs and also the 

 temperature of the soil. Here are some figures for the Argen- 

 tine ant, each figure being an average of twenty individuals. 



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