THE EAT-TAILED FLY, OR DRONE FLY. 269 



by nature. At the present day we are able to execute 

 subaquatic works of great magnitude such, for 

 example, as the Dover piers by means of the diving 

 apparatus. This is nothing more than an imitation of 

 the Rat-tailed larva's air-tube, the diver being sub- 

 merged for hours at a time, and supplied with air 

 through an elastic tube. 



Should anything occur which might alarm the 

 insect, the tail is instantly and swiftly withdrawn, so 

 that scarcely a trace of its presence is left. I once 

 found quite a preserve of these larvse in a neglected 

 water-butt which was nearly filled with dead leaves, dead 

 insects, and other debris. They were so thickly planted 

 in the fetid mud, that their tails looked just like a 

 number of fine grasses set closely together. It was 

 curious to see the effect of a tap on the edge of the 

 barrel. In a moment every tail was withdrawn, and 

 the few inches of water that was left above the mud 

 became on a sudden quite clear and bright. 



The best way of observing the remarkable struc- 

 ture of the telescopic tail, with its double air vessels, is 

 to place one of the grubs with its head downwards in 

 a glass tube, at the bottom of which there is an inch 

 or so of mud. The grub will at once make its way 

 down, and the tube should then be filled with rain- 

 water for some three inches above the mud. The 

 water will soon clear itself, and by means of the mag- 

 nifying-glass the structure of the tail can easily be 

 made out. With a little management this tube may 

 be so arranged as to bring a moderate power of the 

 microscope say the half- inch object-glass to bear 

 upon it. 



