Insects and their world 



Another instance of convergence through similarity of function is the 

 sucking proboscis of the bugs (Hemiptera) and the bloodsucking flies 

 (Diptera) (Figs. 25C5 d). The ancestral insects had mouthparts of a 

 generalised kind, i.e. with the mandibles, maxillae and labium not 

 specially adapted for a particular diet, or way of feeding. Many existing 

 insects that bite or chew their food have the mandibles with a simple 

 cutting edge, and the maxillae and labium as simple lobes to hold and 

 guide the food. All the insects with chewing mouthparts have probably 

 had them throughout their evolution, the beetles as well as the grass- 

 hoppers. On the other hand, those with mouthparts adapted for sucking 

 fluids must have evolved them from the cutting and chewing type. 



Hemiptera are the most highly evolved Order of the Sub-class 

 Hemimetabola, and Diptera are one of the more highly evolved Orders 

 of the Sub-class Holometabola. Their sucking mouthparts must have 

 evolved quite independently, but by convergence they have reached a 

 remarkably similar form and function. 



Mimicry 

 In the examples of convergence that we have discussed, the insects 

 concerned get no advantage from resembhng each other. There are, 

 however, striking instances where two or more unrelated insects have 

 converged in colour and pattern until they look very much alike, and if 

 one or all of them seem to get some advantage from the likeness we say 

 that this is a case of mimicry. 



Stinging Hymenoptera, especially wasps, are dangerous foes to other 

 animals, which mostly leave them alone. Far from conceahng them- 

 selves, the biggest wasps (the Hornet, for example) are boldly patterned 

 and brightly coloured, often in black and yellow, or black and red. This 

 'warning colouration' is like the striking black-and-white pattern of the 

 skunk, which is said to give warning to other animals to keep out of the 

 way. 



If a harmless moth, beetle or fly has a pattern that gives it only a 

 superficial resemblance to a wasp, then it would seem likely that its 

 enemies would be deterred, and the insect would have a better chance to 

 survive. 



This is known as Batesian mimicry. The mimic must live in the same 

 area as the model, and behave in much the same way. Then it is con- 

 sidered that an enemy, such as a bird, or a Hzard, will catch a number of 

 the models and find that they are distasteful or dangerous. After that 

 it will leave them alone. It wiU also leave alone the mimics. The mimics 



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