DIPTERA 



139 



larva of the drone-fly is aquatic and is known as the 

 " Rat-tailed Maggot," on account of the long, tail-like 

 breathing tube. They may be found in masses in stag- 

 nant water. The family, as a whole, may be considered 

 as beneficial. 



92. Bot-flies, Warbles, Gad-flies or Heel-flies as the 

 (Estridce are variously called, 



are parasites of domestic 

 and wild mammals. The 

 adults are usually hairy and 

 somewhat bee-like. The best- 

 known adult is probably 

 that of the Horse-bot, which 

 lays its eggs on horses in 

 late summer and always 

 causes the animals attacked 

 to become excited. Other 

 species attack sheep and cat- 

 tle. (See page 191, Part II.) 

 This family includes most 

 of the insects which are in- 

 ternal parasites of the higher 

 animals. 



Hippoboscidce. These insects are external parasites, 

 in the adult stage, upon mammals and birds. They are 

 either winged or wingless, usually the latter, and have 

 flattened, louse-like, bodies. The larval stages are passed 

 within the bodies of the adult females and emerge from 

 them only when fully grown and ready to transform to 

 the pupa. The so-called Sheep-tick (page 202, Part II), is 

 our most common member of this group. 



93. Muscina. The largest and by far the most im- 

 portant group of flies includes those that were formerly 



FIG. 103. Above, Larva of the 

 Ox-warble ; below, Horse 

 Bot-fly. Slightly enlarged. 



