ANIMAL, PARASITES OF CATTLE. 509 



in the walls of the esophagus, or gullet, and may be found in this 

 location as early as August 15. During the fall and winter a large 

 proportion of the gullets of cattle that are slaughtered are found to 

 be infested with warbles, and are known as grubby gullets or weasands 

 m the packing houses. 



When the warbles first appear in the back they are about f inch 

 long. They cause swellings about the size of pigeons' eggs, each swell- 

 ing having a small hole in the center, which has been punctured in 

 the skin by the warble to enable it to breathe. Tlirough this hole the 

 warble leaves the back of the cow when it has completed its parasitic 

 stage of development, at which time it measures nearly an inch in 

 length. 



The full-gi'own larvae begin to leave the backs of the cattle early 

 in the year, and in northern latitudes the last leave before the mid- 

 dle of July. After leaving the backs of the cattle they bm-row into 

 the ground, he quiescent for about a month, and become trans- 

 formed into mature flies. In northern latitudes the mature flies of 

 the species H. lineatum may be observed duimg April and May, 

 and those of the other species during June and July. 



The damage caused by warbles includes injury to stampeding 

 cattle frightened by the fly, decreased milk flow and diminished 

 growth in infested animals, and injury to hides, the last item being 

 especially serious. 



Treatment. — The best method of control known at present is to 

 Cextract the warbles from the backs of cattle and kill them.~) If they 

 are almost ready to leave the cattle, they may be (^squeezed from the 

 backs with the fingersT) Forceps are useful in removing the warbles, 

 but it is important to be careful in extracting warbles not to crush 

 them, as the body juices of these parasites are sometimes poisonous to 

 cattle if absorbed into their circulation. In the South herds may be 

 examined in November or early in December and once a month during 

 the next two or three months. In the North the first examination 

 may be made six weeks to two months later, with two or, better, 

 three following examinations at intervals of a month. If this pro- 

 cedure is carefully carried out there will be a noticeable diminution of 

 warbles the following year, (and if persisted in the warble can be al- 

 most if not completely eradicated. Where an entire community 

 follows up the practice of removing and destroying warbles, the 

 results are highly beneficial. \ 



As a result of recent studies by various investigators it appears 

 that the tiny grubs, newly hatched from the eggs, may gain entrance 

 to the body by penetrating directly through the skin. Many ob- 

 servers, however, have held that the eggs or newly hatched larvae 

 are taken into the mouth by the cattle licking themselves. It is 



