14 palmers' bulletin Pol. 



flocks is more general. In this country, while a few cases occur 

 nearly ever}' 3'ear following lambing, it is only when favorable 

 weather conditions prevail that the injury becomes serious. In such 

 cases a large percentage of ewes may become infested about the rump 

 following lambing. Some are killed outright, nearly all are cut 

 down in flesh, and the loss in wool sometimes amounts to nearly half 

 of the entire clip on the 6wes infested. The cost of treatment and 

 material used in destroying the maggots is considerable under such 

 conditions. 



Another common place of attack by these maggots is in the wool 

 surrounding the horns. The blowing is usually started by the pres- 

 ence of slight injuries around the horns caused by fighting. Some 

 cases of maggots follow the soiling with excrement of the wool 

 about the vent. This usually occurs when sheep are sick and have 

 diarrhea. 



The eggs are laid on the soiled wool, and the small maggoty 

 upon hatching work into the wool. Many of them feed next to the 

 skin, and soon the avooI is loosened in large patches and the sldn 

 made red and raw. The odor from the infested area is strong, and 

 other flies are attracted to deposit their eggs. As the irritation in- 

 creases the flesh is entered, and the sheep often die. 



SPECIES OF FLIES INVOLVED. 



THK BLACK BLOWFLY.' 



The fly which is responsible for most of the trouble from wool- 

 maggots, especially in the Southwest, is the black blowfl3^ It is the 

 maggot of this fly which is commonly found in old festering sores 

 and following dehorning, except when this operation is done during 

 the summer time in the Southwest, when the screw-worm is the 

 species concerned. 



This fly usually becomes active during warm days in the winter 

 and multiplies rapidly in the early spring, but the hot dry weather 

 of summer soon reduces its numbers so that in the Southwest it maj'^ 

 disappear completely for a few months. It again increases in num- 

 bers during the fall, and after about November 1 largely takes the 

 place of the screw-worm fly as a carrion breeder. 



The adult is about the same size as the screw-worm fly, but it is 

 greenish-black in color and has no stripes on the back. (See fig. 6.) 

 It shoidd not be confused with the large hairy bloAvfly ^ or the blue- 

 bottle flies,^ which are often seen in or around houses during the fall, 



1 Phormia regina Meigen. 2 Cynomyia cadaverina Desv. * Calliphora spp. 



