DIPTERA OK TKUE 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 



Fig. 100.— Wiutek Gnats (Trwhoeera). 

 1, 2, Larva of T. hiemalis; 3, 4, pupa ; 5, 6, imagines ; 7, nat. size. (Curtis.) 



be looked upon as useful insects, helping the speedy decay of 

 roots, &c., in the soil. 



Amongst the Brachycera are some of great importance : only 

 one group can be mentioned here, namely, the 



Gad-flies or Tabanidae. 



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

 head closely united to the thorax (fig. 102, c). They 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 off flowers. The larvae 

 (fig. 102, d) live in the ground, and are vegetarian in habits. 

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

 flies, and Brimps. There are several species very common 

 in Britain, notably Hcemaiopoda pluvialis, Tabanus bovinus, 

 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 



