POPULAR SCIENCE 



THE EVOLUTION OF THE CATERPILLAR 



By HERBERT MACE, F.E.S. 

 I 



In most insect orders, the younger, or larval form, does not 

 vary much from one simple type. The reason for this is 

 quite clear and is, indeed, one of the strongest arguments for 

 the theory that protective resemblance plays a profoundly 

 important part in the outward appearance of animals and 

 plants. Just as the roots of plants, which are underground 

 and not exposed to the risk of discovery by animals which 

 look for them, seldom vary far from the simple cylindrical 

 form, without marked coloration, while the stem and leaves, 

 which are subject to all the influences incident to exposure, 

 vary infinitely : so the larvae of insects, being, for the most part, 

 hidden from view, would not benefit by an approximation in 

 appearance to their surroundings. The larvae of all the bees, 

 living in prepared cells, are much alike. Those of the flies, 

 which are generally deposited in a mass of readily assimilated 

 food, differ onh^ in the possession of slightly varying organs 

 for extracting the nourishment. All these and those of many 

 more orders which pass their lives in a dark retreat, are whitish 

 or neutrally coloured. 



The case of Lepidopterous larvae is very different. In 

 the majority of instances, they are destined to live amongst 

 the leaves of plants of varying species, presenting the most 

 intricate problems of concealment and safety for solution. 



The basis of these problems is the same in all cases. Ade- 

 quate nourishment must be procurable for the duration of the 

 larval stage, which is the only one in which growth takes 

 place, and the vigilant eyes of predatory animals, mostly birds 

 and reptiles, must be eluded. 



II 



As a first step towards the solution of this problem, the 

 majority of caterpillars feed only at night, the number which 



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