FARMERS BULLETIN 857. 



of a biitterflj''. A 

 few kinds of flies 

 have the habit of 

 retaining the eggs 

 within the boch' 

 until they hatch 

 and then deposit- 

 ing the minute but 

 active maggots. 



THE ADULT. OR FLY. 



Of the flies that 

 breed in ^Younds 

 on animals, the 

 screw-worm is of 

 paramount im-f 

 portance, and all' 

 stockmen should 

 learn to distin- 

 guish this fly from others. It is one of the most common of the so- 

 called blowflies in the Southwest during the summer and fall months, 

 although in the summer it is more or less common in practically all 

 parts of the United States. Sometimes it is spoken of by observant 

 stockmen as the " red-head," on account of the rather conspicuoug 

 red or yellowish-red coloring of the face. It is considerably larger 

 than the comm(m house fly, of a dark bluish green color, with three 

 distinct black stripes on the back between the wings, as shown in 

 figure 1 and on the title page. 



Fig. 2.^Esrg:s of the screw-.worm fly. Greatly enlarged. 



The eggs of the screw-worm fly are very similar in appearance 

 those of other blowflies. They are about a sixteenth of an inch lonj 

 and creamy white in color. Most of them are somewhat curved and* 

 have a slightly projecting double ridge along one side. (See fig. 2.)^ 

 They are laid in irregular masses, sometimes several thousand^ 

 being deposited in 

 a ma.ss by a num- 

 ber of females. 



THE LARVA. OR 

 MAGGOT. 



The maggots 

 of the flies which 



infest wounds or j^n.. 3. — Serew-wonn ina.:,'f;ot. side view. Enlarged. 



ii 



