DU'TEKA OR TRUE FLIES. 207 



the head end, about half an inch long, and dirty greyish-yellow 

 in colour. They need no further comment, except that they may 



Fic. 100. — Winter Gnat.s (TricJioceru). 

 1, 2, Lar\a of T. hiemcdis ; 3, 4, pupa ; 5, 0, iinafjines ; 7, iiat. size. (Curti.s.) 



be looked upon as useful insects, heli)ing the speedy decay of 

 roots, &o., ill the soil. 



Amongst the Brachyoera are some of great importance : only 

 one group can be mentioned here, namelj", the 



Gad-flies or Tabanidse. 



Gad-flies are large flies with a flattened body and large broad 

 head closely united to the thorax (fig. 102, c). The}- are all 

 provided with a sharp piercing mouth (fig. 101, b), with which 

 they suck the blood of horses and cattle. The females are 

 especially bloodthirsty ; the males feed ofl' flowers. The larvas 

 (fig. 102, u) liv(! in the ground, and arc vegetarian in habits. 

 They are known under the names of Horse-flies, ISreeze- 

 flies, and Brimps. There are several species very common 

 in Britain, notably Haimatopoda plumalis, Tahanus hovinus, 

 and T, autumnalis. The first named is about half an inch 

 long, whitish-grey, covered with pale dull hairs in the female, 

 dark grey in the male, wings mottled grey. The latter two 



