4 FARMERS BULLETIN 857. 



abundant in the Nortliern States, and the fly itself is killed quickh' 

 by cold weather. Since 1843 it has been of more or less importance 

 nearly every year in what are now the Southwestern States. At 

 times it has become a serious pest farther to the north and east. For 

 instance, in 1890 a rather seA^ere outbreak was experienced in Lou- 

 isiana and Mississippi, and very frequently it causes much annoyance 

 to stock in Kansas. 



In the Southeastern States cases of screw-worm injury are in- 

 frequent. 



The seasonal abundance of the screw-worm fly depends largely 

 upon climatic conditions. The first appearance of adults in num- 

 bers in spring varies from the first of April to the middle of June, 

 according to the latitude and earliness or lateness of the season. 

 Throughout most of the territory where it is a pest it usually be- 

 comes numerous during early May, and cases of screw-worm injury 

 begin to appear soon after. The insect then gradually increases in 

 numbers until the hot, dry weather of midsummer, which in Texas 

 usually reduces the abundance so that the injury is not severe under 

 normal conditions in the months x)f July and August, unless consid- 

 erable cloudy and rainy weather occurs. It becomes more numerous 

 again in the early fall, especially when the weather is warm and 

 showery, and its activities are terminated only with the advent of 

 heavy frosts. The abundance of this fly, of course, is dependent to 

 a large extent upon breeding places at hand, but it is also true that 

 a warm, humid atmosphere is best suited to its development. 



CHARACTER OF INJURY AND LOSSES DUE TO THE SCREW-WORM. 



Practically all animals are more or less subject to attack by the 

 screw-worm. Probably cattle suffer most, with hogs, horses, mules, 

 sheep, goats, and dogs following in the order named. Wild deer 

 and many of the smaller mammals sometimes are seriously infested. 

 Numerous cases of infestation of human beings have been recorded, 

 and probably thousands of such cases have not been reported. 



In man the nose and throat are most commonly infested, the cases 

 occurring usually among individuals who suffer from chronic catarrh. 

 Minor wounds on various parts of the body also are infested. 



Among live stock the most common form of attack follows minor 

 skin injuries, such as cuts by barbed wire and scratches from brush 

 or from hooking. Sometim-es calves are attacked by the Avorms at 

 the time of birth. In these cases the screw-worms may enter on 

 various parts of the body, but most commonly at the navel, where 

 they penetrate with ease. If not promptly treated, the calf may die. 

 Later in the life of the calves it is not infrequent to find infestations 

 of the mouth, in some cases resulting in the loss of teeth or death. 



