374 THE ATHERICERA. 



them into the air and devouring them. In this 

 way the larvae of the species above referred to^ which 

 is found upon the rose^ will often clear a bush com- 

 pletely of all the Aphides which usually infest its 

 twigs in such numbers. When full-grown^ the larvae 

 attach themselves to the leaves or stems of the plants 

 on which they have been carrying on their appointed 

 work of destruction, and undergo their change to the 

 pupa state, when the larva-skin contracts and dries as 

 usual, forming a case for the protection of the pupa. 



These, however, are the habits only of the species 

 of the genus Syrphus ; those of many nearly allied 

 species are exceedingly diflPerent. Thus the larvae 

 of the genus Volucella, the perfect insects of which 

 are generally of considerable size, reside in the nests 

 of Humble Bees and Wasps, upon the larvae of which 

 they prey ; that of Rhingia rostratttj a curious species 

 with the front of the head produced into a beak, 

 furrowed beneath for the reception of the long geni- 

 culated proboscis, lives in horse-dung; whilst those 

 of Eristalis and Helophilus are found in dirty stag- 

 nant water, drains and cesspools. The structure of 

 the latter larvae is very remarkable, and admirably 

 adapted for the pecidiar situations in which they 

 reside. Constantly engaged in seeking their food 

 amongst the mud at the bottom of shallow pools of 

 water, they of course require to be kept in some way 

 in communication with the air at the sm-face, and 

 this is effected by means of an elongated tail, which 

 is not only capable of stretching to a great extent, 

 but also includes an inner sliding tube, like that of a 

 telescope, so that when the whole organ is fully drawn 

 out, it is sometimes nearly twelve times the length 

 of the body of the animal. At the extremity of the 



■f. ' 



