HOUSE-FLIES 105 



proved to be common house-flies (M. domestica), and I 

 suspect that they have become so artful by haunting 

 horses ; at all events this species does annoy horses a 

 great deal. 



How do we tell the common house-fly from other flies 

 of much the same general appearance ? One distinctive 

 mark is found in the colour of the abdomen, which in the 

 common house-fly is always yellowish at the base, and 

 often over a great part of the under surface. If we 

 separate the very peculiar antenna from the front of the 

 head, and examine it with a lens, we shall see that the 

 long bristle, which forms its proper termination, is 

 feathered, whereas in some other house-flies it is naked. 

 The upper surface of the thorax shows dark longitudinal 

 streaks in many flies, due to absence of the hairs which 

 elsewhere hide the dark skin. In the common house-fly 

 four regular and distinct streaks run lengthwise along the 

 back of the thorax, but are not continued upon the grey 

 semicircular shield (scutellum) at the hind end of the 

 thorax ; another dark streak, broader in the female than 

 in the male, runs along the middle line of the back of the 

 abdomen. All this particularity is necessary in order to 

 distinguish with certainty the common house-fly from 

 other flies which are often met with in houses. 



The common house-fly often hibernates in cellars and 

 attics. In a mild winter some of these semi- torpid flies 

 make their way from time to time into the living rooms, 

 and I think I have seen them in nearly every month of 

 the year. 



The larva is bred in horse- dung ; or, as some naturalists 

 tell us, in decaying vegetables. It is like the maggot of 

 -the blow-fly, though much smaller. It pupates within 

 the larval skin after one week of larval existence, and the 

 fly appears at the end of the second week. 



The common house-fly is often infested with mites, or 

 with false-scorpions (Chelifers), one species of which 

 (Chernes nodosus) has often been found on the legs of flies. 



