(ECOLOGY. 357 



the warfare between insects of different kinds, by the 

 numerous insects parasitic on others, by the appetite of 

 higher animals, fishes, frogs, ant-eaters, insectivores, and, 

 above all, birds. 



There is a great variety of protective adaptation. The 

 young of caddis-flies are partially masked by their external 

 cases of pebbles and fragments of stem ; many caterpillars 

 and adult insects harmonise with the colour of their environ- 

 ment; leaf-insects, "walking sticks," moss-insects, scale- 

 insects, have a precise resemblance to external objects 

 which must often save them; a humming-bird moth may 

 resemble a humming-bird; many palatable insects and 

 larvae have a mimetic resemblance to others which are 

 nauseous or otherwise little likely to be meddled with. 

 Many insects may be saved by their hard chitinous armour, 

 by their disgusting odour or taste, by their deterrent 

 discharges of repulsive formic acid, etc., by simulation of 

 death, by active resistance with effective weapons. 



Many flowers depend for cross-fertilisation upon insects, 

 which carry the pollen from one to another. Many insects 

 depend for food on the nectar and pollen of flowers. Thus 

 many flowers and insects are mutually dependent. But 

 many insects injure plants, and many plants exhibit 

 structures which tend to save them from attack. On the 

 other hand, there may be "partnerships" between insects 

 and plants as in the " myrmecophilous " (ant -loving) 

 plants, which shelter a bodyguard of ants, by whom they 

 are saved from unwelcome visitors. And again, the 

 formation of galls by some insects which lay their eggs 

 in plants, and the insect-catching proclivities of some 

 carnivorous plants, should be remembered. 



Most insects are terrestrial and aerial ; the majority live 

 in warm and temperate countries, but they are represented 

 almost everywhere, even above the snow-line, in arctic 

 regions, in caves. Even on the sea the Challenger 

 explorers found the pelagic Halobates, a genus of bugs. 

 The distribution of insects is mainly limited by food- 

 supplies and climate, for their powers of flight are often 

 great, and their opportunities of passive dispersal by the 

 wind, floating logs, etc., are by no means slight. 



Many insects are more or less parasitic, either externally 



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