54 A BOOK OF INSECTS 



which fits into a socket in the thorax ; second, a small 

 joint called the trochanter, which in some cases is divided 

 into two ; third, the thigh or femur ; fourth, the shin or 

 tibia ; fifth, the foot or tarsus, which normally consists of 

 five joints, although the number is sometimes four or 

 three, and in exceptional cases two or even one. The 

 last joint is provided with a pair of claws. 



The legs of insects have been subjected to the greatest 

 modification in accordance with the special requirements 

 of their owners. In the mole-crickets, the fore-legs are 

 elaborate burrowing implements, the tibia and tarsus being 

 so arranged that they act as shears for cutting roots. 

 Some insects have become quadrupeds so far as walking 

 is concerned owing to the specialisation of their fore-legs. 

 In the so-called praying mantis, or rcarhorse, the fore- 

 legs constitute a kind of trap which is used for seizing 

 prey ; a somewhat similar contrivance is seen in the case 

 of water-scorpions ; while in many butterflies the fore- 

 legs are greatly reduced in size and quite useless for walk- 

 ing. The middle legs are not usually greatly modified, 

 but in some water-bugs they are the longest and strongest 

 of all the legs, and are used as sweeps, by means of which 

 the insect propels itself through the water. In most 

 aquatic insects, however, the hind-legs are the chief means 

 of propulsion. The hind -legs of grasshoppers and locusts, 

 as well as certain beetles, are very long and powerful, 

 enabling the insect to spring high into the air. 



In many insects the legs serve certain minor purposes 

 unconnected with locomotion. Thus, in many beetles a 

 cavity in the front shin, lined with bristles, serves as a 

 comb for cleaning the antenna? ; while in the case of bees 

 and wasps there is a still more elaborate contrivance for 

 the same purpose near the upper end of the first tarsal 

 segment. Again, the abortive fore-legs of many butter- 



