358 THE MECHANICAL FUNCTIONS. 



formed by the expansion of the tail, enabling 

 them to steer their course with more certainty. 

 The Lepidoptera in general fly with the body 

 nearly upright, contrary to the habits of most 

 other winged insects, whose bodies, while flying, 

 are nearly in a horizontal position. 



The feats of agility and strength exhibited by 

 insects have often been the theme of admiration 

 with writers on natural history ; and have been 

 considered as affording incontrovertible proofs of 

 the enormous power with which their muscles 

 must be endowed. We have already had occa- 

 sion to notice a remarkable instance of the force 

 and permanence of muscular contraction in those 

 caterpillars which frequently remain for hours 

 together in a fixed attitude, with their bodies 

 extended from a twig, to which they cling by 

 their hind feet alone.* Ants will carry loads 

 which are forty or fifty times heavier than their 

 own bodies : and the distances to which many 

 species, such as the Elater, the Locust, the 

 Lepisma, and above all the Pulex, are capable 

 of leaping, compared with the size of the insects 

 themselves, appear still more astonishing. Lin- 

 naeus has computed that the Melolontha, or 

 chaffer, is, in proportion to its bulk, more than six 

 times stronger than the horse : and has asserted 

 that if the same proportional strength as is pos- 



* See Fig. 148*, p. 315. 



