HOUSE FLIES AND BLUEBOTTLES 173 



wings slightly tinged with grey. But this first impres- 

 sion will be corrected by a closer scrutiny, which will 

 discover many quiet beauties of one kind and another. 

 Two of the chief items which determine the personal 

 appearance of a fly belonging to this group are stiff 

 projecting hairs (or rather bristles), and what at first 

 looks rather like a kind of rime; but on microscopic 

 examination turns out to be crowds of exceedingly 

 minute hair-like or scale-like bodies lying close to the 

 skin. The latter are mainly instrumental in producing 

 whatever colour forms patterns or markings upon the 

 otherwise frequently dull bodies of flies, while the vary- 

 ing size and number of the former exercise an important 

 influence upon the general aspect of the insect, and make 

 all the difference between a sharply defined and an 

 indistinct outline of the body. 



The skin of the house fly, on the upper surface, is in 

 itself chiefly black ; but the rimy covering (called col- 

 lectively " tomentum "), which is scattered pretty thickly 

 over it in most parts, gives it a greyish spotted appear- 

 ance on the abdomen, causes also the resemblance of 

 four dark lines of the thorax, where bare spaces are 

 left, and beautifully adorns the face with a bright 

 silvery covering. The large compound eyes are of a 

 vinous red, and present a pretty contrast to the soberer 

 colours of the rest of the insect. Underneath, the fly is 

 quite pale, i.e., the ground colour of the skin itself is 

 pale, as well as the tomentum. Its bristles are not 

 sufficiently large or numerous to become a noteworthy 

 feature in its aspect. It has no power of stinging or 

 piercing, and, therefore, is not a bloodsucker, and simply 

 worries us by the tickling sensation it produces when 

 trying to sip the perspiration from our hands or face, 

 or when simply running over the exposed parts of our 



