INSECT A : DIPTERs 



333 



Volucella. 



then separating from its skin, which forms a rather pear- 

 shaped white case round the body, which is transformed 

 within. The fly emerges in about ten days; it is at first 

 small with tightly crumpled-up wings, but in a quarter of an 

 hour it attains its final state. 



Volucella is another common species of Syrphid. 

 It lays its eggs inside the nests of humble-bees or 

 wasps, and it used to be thought that the larva fed on the 

 young bee and wasp larvae. Recent investigations, however, 

 seem to show that this is not so, but that the Volucella larvae 

 are useful to their hosts, for they 

 act as scavengers, feeding on the 

 waste matter and dirt of the 

 hive. 



Eristalis Eristalis, another 

 tenax (the member of the Syr- 

 Drone -fly), phidae, is peculiar in 

 having an aquatic larva of a very 

 interesting and unusual type. 

 This black, hairy " Drone-fly " is 

 rather bee-like in form ; it is a 

 strong, active fly, a little over J 

 an inch long. It lives on the 

 honey and pollen of flowers, quit- 

 ting, however, the fresh sunny 

 garden, to lay its little packets 

 of white eggs on the surface of 

 the dirtiest, most putrid water it 

 can find, often in a manure tank. 

 The larva, when it hatches out, 

 spends its time creeping over the 

 mud and debris at the bottom, 

 feeding on the decaying organic 

 matter, but always keeping up 

 communication with the air above 

 the water, by means of the curious 

 telescopic tail through which it breathes. This stage is a 

 strange contrast to its later life, when it flies freely in a garden, 

 and we are perhaps inclined to think of it as an undesirable 

 inhabitant of our tanks, though, as a matter of fact, it lessens 

 rather than increases the putrid condition of the water by 



FIG. 253. Eristalis tenax. 



E, Eggs ; L, larvae, " rat-tailed mag- 

 gots " of two ages, one crawling 

 on the mud, the other suspended 

 from the surface. 



