618 INSECTS AT HOME. 



large wings, and humming flight. Moreover, it has a bec^-lil^e 

 habit of moving its abdomen up and down as if threatening to 

 use a sting, and in consequence of this resemblance it is very 

 needlessly dreaded by the generality of those who see it. Its 

 colour is variable, but is generally some shades of brown, grey, 

 and black. It is very swift on the wing, and has a quick- 

 darting flight much resembling that of the Humble-Bee Fly, 

 which has just been described. 



The larva is a most curious being. It is a worm-shaped 

 grub, the tail of which is prolonged into a wonderfully long 

 telescopic tube, by means of which the creature breathes, the 

 air-tubes passing through it exactly as was related of the gnat 

 larva. When this telescopic tail is prolonged to its greatest 

 extent, it is about as thick as an ordinary pin. Owing to the 

 transparency of its walls, the double air-tube within it can be 

 easily seen, and when the tail is elongated so are the air-tubes. 

 But when the larva is frightened and contracts its tail, tlie air- 

 tubes may be seen doubled up in an apparently complicated 

 but really simple manner, just below the base of the tail. As 

 may be supposed, when a telescopic tail of more than two 

 inches in length is suddenly shut up and reduced to a nullity, 

 the elastic air-tubes within it must undergo a process of 

 folding. This is done with such precision that the tail can be 

 gradually extended or smartly closed over and over again, and 

 yet not one single fold of the enclosed air-tubes ever hitches 

 over another so as to impede the play of the all-important 

 tubes. 



This may appear a very simple matter, but it is in fact a 

 very complicated one, as may be seen from the following 

 parallel. Suppose that an ordinary telescope were drawn out 

 to its fullest extent, and that two india-rubber tubes were 

 stretched inside it, parallel to each other. Now if the telescope 

 be closed, tlie tubes fall of necessity into coils in the lowest and 

 largest joint of the telescope. Open the telescope again, and 

 the two tubes will again be straight and parallel, provided that 

 they have not interfered with each other while they were coiled 

 up together at the bottom of the telescope. Let but one single 

 coil envelope another, and either the telescopic joints cannot 

 be opened, or one of the tubes is snapped. 



I have dissected numbers of these larvas, and have always 



