The diversity of insects 



Fig. 69. Head of an 

 aphid. Order Hemiptera- 

 Homoptera, showing the 

 compound eyes, small, 

 yet consisting of many 

 hexagonal facets 



Beetles, on the other hand, all bite and chew their food, and have kept 

 the primitive kind of mouthparts. 



Legs, again, are used by insects for a variety of purposes, and have 

 been developed in a number of different ways. In their simplest form 

 they are used for walking and running, and the femora, tibiae and seg- 

 ments of the tarsi are slender, without any peculiar spines or swellings. 

 Insects that dig in the ground often have the fore-legs shorter, broader 

 and stronger, as in some ground beetles (Carabidae), chafers (Scara- 

 baeidae) and dung beetles (Geotrupidae). Such adaptations are usually 

 on the fore-legs only, and these do the work of digging while the insect 

 is supported on the other two pairs. The fore-legs of the mole cricket 

 (Gryllotalpa, Fig. 2) are an extreme development. 



Predatory insects, which catch other insects as food, also generally 

 use the fore-legs for this purpose. The Order Hemiptera includes 

 several famiHes of predatory bugs, which may have the fore-legs 

 specially developed for seizing and holding the prey. Fig. 51a shows 

 one of these, which must be a fearsome instrument against a smaller 

 insect. The best known 'raptorial fore-legs' of this kind are those of the 

 praying mantids (Fig. i). Robberflies (Asilidae) catch their prey in 

 flight, but generally have all three pairs of legs strong and hairy. In the 

 air the legs hang down like a spiny basket, which envelops the prey so 

 that it cannot escape (Figs. 50, 72). 



Ill 



