The diversity of insects 



Fig. 72. Not a bee, but a robberfly. Order Diptera, which mimics a bee 



must be much less nimierous than the models, otherwise the enemy will 

 find that it can eat some of them. 



An example of Batesian mimicry is provided by some African robber- 

 flies called Hyperechia (Fig. 72). These are large, fiercely carnivorous 

 flies, which prey upon the equally large and fierce carpenter-bees of the 

 genus Xylocopa. The flies have evolved a shape and colour that is not 

 merely like a Xylocopa, but which quite uncannily resembles the parti- 

 cular species of the bee that the fly attacks. Thus protectively camou- 

 flaged, the adult robberfly can move among the bees, to catch and kill 

 them, and to lay its eggs near the burrow, so that its larvae can go inside 

 and feed on the larvae of the bees. 



There are several species of Hyperechia, each preying on a Xylocopa, 

 which it closely resembles. The odds against this arising by mere chance 

 are impossibly great, and there can be no doubt that, in this case at 

 least, the advantage to the fly has been great enough to bring about this 

 mimetic resemblance by natural seleaion. Not all mimics copy their 

 model so well as Hyperechia does, but this is an exceptional case, where 

 the fly has to deceive the model itself, and to go among the bees without 

 their being aware of it. Most mimics do not deceive the model, but its 

 enemies, and they do not need to be good enough to stand up to close 

 examination. All that is necessary is that an enemy should be made to 

 hesitate for a brief moment, during which the mimic can escape. 



There is a second kind of mimicry, which is said to exist between 



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