DIPTERA. 



53 



eggs therein. When these eggs have hatched, the larvae, which have 

 the mouth armed with two mandibles, devour the larvae of their 

 hosts, the bees. This is the return 

 they make for the hospitality they 

 have received ! 



The Helophili (Fig. 39; deserve 

 to be mentioned here on account 

 of the singular form of many of 

 their larvae. The head is thick, 

 fleshy, and varying a little in form. 

 But the point by which they are 

 easily to be distinguished from 

 most other larvae is, that they have 

 always very long tails, sometimes, Fi s- 39- A species of Heiophiius. 

 indeed, out of proportion to the 



length of the body. Re'aumur called these larvae " vers a queue de 

 rat;" they. are known in England as rat-tailed maggots, and their 



Fig. 40. Larvse 01 a Heiophiius 



habits are aquatic. Having placed some or them in a bason of 

 water, Reaumur saw that they kept in a perpendicular position at 

 the bottom of the bason, and parallel to one another, the extremities 



