6 INTRODUCTION. 



appears to have reached its furthest stage, winged and apterous 

 forms, and sexual and sexless (or possibly perfect hermaphrodite ?) 

 forms, succeeding each other alternately. 



Among the curious phenomena presented to us by insect life, 

 those connected with protective resemblance, and above all, 

 mimicry, are not the least remarkable. Many insects present a 

 striking resemblance to other natural objects, as leaves, sticks, 

 seeds, lichen, bird-droppings, etc., and thus escape the notice of 

 their enemies. Others resemble various insects which either 

 enjoy an immunity from the attacks of certain enemies, or are fur- 

 nished with means of defence. Thus a beetle may resemble 

 an ant, or a moth may resemble a wasp, or a butterfly (or 

 perhaps only its female) may resemble a butterfly of a different 

 family which is protected from birds by an unpleasant smell and 

 taste ; and in extreme cases this resemblance is so close that the 

 two insects can hardly be distinguished from one another, except 

 by structural characters, although there may be no real affinity 

 between them. 



Insects are usually abundant in proportion to the exuberance 

 of the vegetation, but the richer the native fauna of any country, 

 the poorer will it become when that is destroyed. Hence it 

 happens that cultivated districts in the tropics often disappoint the 

 collector very much ; while a dense tropical forest, with its dim 

 shade cast by the crowns of the trees a hundred feet above, is 

 anything but rich in insects, though they will swarm in a new 

 clearing, or in other favourable localities. In temperate climates 

 the insects which have maintained their ground as inhabitants of 

 the country are tolerably equally distributed over it in suitable 

 localities ; but even here the draining of marshes and felling of 

 forests speedily exterminates species which inhabit such localities. 



Although insects reach their maximum of size and brilliancy 

 in tropical countries, yet it does not follow that size and brilliancy 

 distinguish all tropical productions. Whole families consist 

 chiefly of small and dingy species, and the number of large and 

 conspicuous species in the tropics is below rather than above the 

 average of those of temperate climates; and although, on the 

 other hand, some families consisting almost exclusively of large 

 and brilliant insects are confined to the tropics, yet the tropical 

 representatives of insects found in temperate climates are frequently 

 inferior to the latter, both in size and colour. Variety of vegeta- 

 tion is more necessary to insect life than great heat ; and many 



