D. TWO-WINGED FLIES (DIPTERA) 

 23. THE HARLEQUIN-FLY (Chironomus) 



There are few commoner insects than this. The larva, 

 which from its deep red colour is popularly called the blood- 

 worm, abounds in slow streams, particularly in the foul 

 streams which flow near towns and cities. The pupa is 

 aquatic too, but the fly is a delicate, gauzy creature, gnat- 

 like in appearance, which is often seen upon the window- 

 pane in summer. It belongs to the same order as the gnat 

 — the Diptera, or two-winged flies. The larva is not large 

 enough for ordinary dissection, being only an inch long at 

 most, and very slender. It has, however, the great advantage 

 of transparency. Any student who can command a micro- 

 scope will be able to see more internal structure in this small 

 larva than he is at all likely to discover in the largest 

 caterpillar. A second reason for selecting this particular 

 type for examination is that it is reared with great facility. 

 A few dead leaves in a saucer of water suffice for all its 

 wants, and the life-history can be followed throughout on 

 the easiest possible terms. 



Having found a stream, a water-butt or a garden-tank which 

 harbours the larvae, pick up a few, either with a dipping tube, 

 or a spoon tied to a walking-stick, as may best suit the place 

 of abode, and bring them home. Observe the looping move- 

 ment by which they swim about, and the anxiety which they 

 show to conceal their bodies. They weave together bits of 

 leaves, or any other particles which lie about, with viscid 

 threads. Where circumstances allow, they make burrows 

 or tubes in mud. A very small larva is best for microscopic 

 study. Place one in water on a glass slip, and cover it with 

 a glass circle. A little cotton-wool may be teased out in the 

 water beforehand, so as to imprison the larva and take off" 

 the weight of the cover-glass. Be careful not to introduce so 



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