Insects and their world 



Fig. 71. A leaf-butter- 

 fly. Order Lepidoptera, 

 showing the undersides 

 of the wings, which 

 resemble a leaf, and are 

 exposed when the 

 butterfly is at rest 



or they may be needed to fold up the hind-wings, which are elaborately 

 pleated, like a fan. 



Bugs of the family Membracidae have the prothorax' enormously 

 enlarged, often into a spiky, shield-like structure. Sometimes this may 

 help to make the insect inconspicuous on a thorny plant, but many 

 Membracids have an ornate structure that seemingly serves no obvious 

 purpose. Similarly, the huge, bulbous head of some Fulgorid bugs, was 

 at one time thought to be luminous, and gave them the name of 'lantern 

 flies', but it now seems to be without any known function. 



The stag-beetles (Lucanidae), with their big mandibles, especially in 

 the males, and the rhinoceros beetles (Dynastinae), with their great 

 horns on the head of the male, seem to be handicapped with clumsy 

 structures that serve Httle or no useful purpose. They bring to mind 

 pictures of the great horned dinosaurs, which became extinct in 

 Cretaceous times, at the end of the age of reptiles. Their appearance 

 suggests that in insects, too, evolution is not always strictly utihtarian. 

 Theories of evolution emphasise adaptation, and the way in which 

 structures arise in response to a need, or in a way that gives their 

 possessors an advantage in the struggle for existence. It seems that 

 sometimes an evolutionary process having started in one particular 

 direction, may continue far beyond what is needed, and produce a 

 structure that is merely a burden to the insect. 



Another peculiarity of evolution is the way in which one insect may 



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