230 OUR HOUSEHOLD INSECTS 



once in position to take a header into the watery world 

 in which it has to pick up its living. 



These larvae (Plate TV.) are odd-looking objects, fore- 

 shadowing the form of the adult to a somewhat greater 

 extent than is usually the case with those insects which 

 pass through a complete metamorphosis. The three 

 regions of the body are distinctly marked out, quite 

 the reverse of what obtains amongst the " short- 

 horned " flies, whose shapeless " maggots " we described 

 in the preceding chapter. If we imagine the full-grown 

 gnat's body to be bereft of all its long appendages 

 wings, legs, antennae, and beak and to be provided at 

 intervals with tufts of hair instead, we get some idea 

 of the outline of the larva. They move by a series of 

 jerks, accomplished by swaying the body from side to 

 side, and the natural position is head downwards. 

 Though living in the water they inhale air, and hence 

 come to the surface occasionally to breathe. The en- 

 trance to the breathing tubes is at the end of a sort 

 of arm or branch jutting out from the hinder, i.e., the 

 upper, end of the body, and all that is necessary for 

 taking in a fresh breath is to expose this little orifice 

 just above the surface of the water. The larva is fur- 

 nished with biting jaws, and spends a good deal of its 

 time in devouring all sorts of rubbish and decaying 

 matters, such as may be found in abundance in the 

 pond it inhabits. Thus it swims about with tail most 

 appropriately pointed to the sky, and head to the muddy 

 bottom, where lie its chief stores of food. 



It is easy to understand that thousands of these larvae, 

 working away in a pond on the decaying organic matter 

 there, will do a good deal towards arresting the pollu- 

 tion of its waters, and gnats, therefore, in this stage of 

 their life, may be regarded as sanitary agents, of more 



