DJPTERA. 477 



Family CESTRID^; (CEs'tri-dae). 

 The Bot-flies. 



This family includes flies that are large or of medium 

 size ; most of the species resemble bees in appearance ; 

 some, the honey-bee ; others, bumblebees. In the vena- 

 tion of the wings they closely resemble the Muscidae ; but 

 the wings are usually furnished with fine transverse wrinkles. 

 They are most easily distinguished from the Muscidae by 

 the small size of the opening of the mouth and the rudi- 

 mentary condition of the mouth-parts, the proboscis being 

 rudimentary and the palpi usually wanting. 



The head is large, with the face broad. The antennae 

 are small, three-jointed, more or less concealed in a suban- 

 tennal cavity or grooves ; the last segment bears a dorsal 

 bristle. Vein III of the wings is three-branched. Cell III 6 

 is broadly open (Fig. 584), or is narrowed at the margin of 



Vj + VII, 



FIG. 584. Wing of Gastrcphilus. 



the wing, or closed. The alulets are usually large, conceal- 

 ing the halteres ; but sometimes they are small. 



The larvae are parasitic upon mammals. The best known 

 species are the following : 



The Horse Bot-fly, Gastrophilus equi (Gas-troph'i-lus 

 e'qui). The adult fly closely resembles the honey-bee in 



