22 



ELEMENTARY ENTOMOLOGY 



Legs. The legs articulate with the sternum and pleurum and con- 

 sist of five parts, - - the coxa, trocJiantcr, femur, tibia, and tarsus. 

 The base of the coxa forms the joint of the leg to the body, which 



is either of the ball- 

 and-socket or of the 

 hinge type. The tro- 

 chanter is a small, in- 

 termediate segment, 

 which in parasitic Hy- 

 menoptera is double. 



Tdr 



Tb 



Tr 



Emp 



~Cla 



FIG. 24. Typical insect leg 



Cx, coxa ; Cla, claws ; Emp, empodia ; F, femur ; Tar, tarsal 



segments ; Tb, tibia ; Tr, trochanter. (After Snodgrass, 



United States Department of Agriculture) 



The * femur is the 

 largest segment in 

 the leg, and in grass- 

 hoppers and other 

 jumping insects is 

 strongly developed 

 by the muscles with- 

 in. The tibia is usu- 

 ally long and slender. The tarsus is usually composed of several 

 similar segments, five being the typical number. The last segment 

 usually bears a pair of sharp claws in adult insects and a single 

 claw in larvae. Between the claws of most adult insects is a little 

 pad, called a pulvillus, or empodium, a suckerlike organ which 

 enables them to walk upon smooth surfaces and to cling to objects 

 when upside down. 



Nearly all adult and most larval insects have three pairs of 

 thoracic legs, but many boring and parasitic larvae have lost them 

 entirely. The legs are often greatly modified according to the habits 

 of the insect, not only for locomotion, but for grasping, digging, and 

 other purposes. The legs of most beetles are typical of walking 

 insects. In jumping insects, like the grasshopper and flea beetles, 

 the hind femora are greatly developed. In digging insects, such as 

 the mole cricket and cicada nymphs, the tibia and tarsus of the fore- 

 legs are developed as shovels. The forelegs of many predacious 

 insects, such as the mantis, assassin bugs, and others, bear teeth 

 upon the opposing surfaces of the tibia and femur, which make 

 them efficient grasping organs. The legs of the bees are highly 

 developed : the forelegs bear a comb for cleaning the antennae, 



