436 THE NATURAL HISTORY 



thus seize their unresisting victims. When full fed 

 each larva fixes itself, by means of a glutinous secre- 

 tion, to the leaf on which, in less than a fortnight, it 

 has completed its useful task, its body then contracts 

 into a pyriform mass, and the usual transformations 

 take place within its hardened skin, which thus serves 

 as an ordinary cocoon. 



The larva of the Drone fly is that curious creature 

 well known as the rat-tailed grub, swarming in shallow 

 stagnant water, turbid with fecal matter and other im- 

 purities. The constant position of this grub in the 

 fluid it inhabits, is, like that of the larvae of Culex and 

 Stratiomys, with its head downwards, but as it differs 

 from the latter in the sluggishness of its habits, its 

 respiratory apparatus is modified to suit this con- 

 dition. The external portion of this apparatus con- 

 sists of two tubes, one sliding within the other like 

 the joints of a telescopic tube, and capable of being 

 lengthened out or shortened at the will of the animal, 

 to suit the varying depth of the fluid from which it 

 derives its sustenance. The spiracle at the extremity 

 of the inner tube, which projects beyond the other, is 

 always in contact with the air at the surface, and it 

 has been ascertained by experiment that these tubes 

 can be drawn out to twelve times the entire length of 

 the body of the grub. When it has attained its full 

 development as a larva, it leaves the water and passes 

 its next stage in the earth, from which, in due time, it 

 makes its appearance in the perfect state. Eristalis 

 tenax, a living specimen of which is now on the table 

 before us, presenting a sad contrast to its former self 

 when revelling in the sunshine, Eristalis intricarius, 

 Eristalis flor ens, all very much resembling the male of 

 the hive bee, and many other species of the genus, 

 are very common here. 



Volncella pellucens, a handsome insect with clouded 

 wings and a transparent patch on the upper surface of 

 its abdomen, is an example of the Bee fly. Its larvae 



