340 DISEASES OF CATTLE. 



fear generally, follow to the water or run off to different parts of the 

 field. 



The larva of this fly, when young, is smooth, white, and transparent; 

 as it enlarges it becomes browner, and about the time it is full grown 

 it is of a deep brown color. The larva, having attained its full growth 

 and size, effects its escape from the abscess in the back of the affected 

 animal, and falls to the ground; it then seeks a retreat in which 

 to pupate. The puparium is of a dark brown color, narrower at one 

 end than at the other, flat on one side, and very round and convex on 

 the other. They may remain in this state for about six weeks, when 

 the fly appears. The grubs usually escape during the months of May 

 and June; occasionally as late as September. Sometimes these warbles 

 are very numerous, and cause a great deal of pain and uneasiness in 

 the animal, which becomes thin in flesh, hidebound, and feverish; 

 more frequently, however, they do no harm, except to the hides. I am 

 under the impression that the so-called heel-fly of our southwestern 

 States and the gadfly are identical. I have never had an opportunity 

 of learning the true history of the former, therefore I can not be 

 explicit. 



Treatment. Whenever cattle have these tumors along the back- in 

 the winter, it is advisable to enlarge the opening which already exists 

 and press out the grub, or it may be caught with the point of a shoe- 

 maker's awl and extracted. 



Since writing the foregoing history of the development of the grub, 

 I have seen an article written by Dr. Cooper Curtice, published in the 

 Journal of Comparative Medicine and Veterinary Archives, Vol. xii, 

 No. 6, in which he details quite a different history concerning the ox- 

 warble, viz : He discovered that the Hypoderma bovis is not the common 

 species of gadfly that we have in this country, but that it is the Hypo- 

 derma Uneata Villers, which is common with us. He says: 



The adult fly lays its eggs somewhere oil cattle, presumably the back, by attach- 

 ing them to the hairs. This attachment is admirably outlined by the structure of 

 the egg, which is similar to that of the horse botfly, Gastrophilus equi, and by the 

 structure of the ovipositor, which is not adapted for boring. While some authors 

 have contended that the egg is laid in the skin others have conclusively shown that 

 this is not the case. * * * Development takes place within the egg while yet 

 attached to the hair. * * * From this point on my version of the life history 

 varies from that of others until the larva has arrived at its destination in the cysts, 

 under the skin, which open to the air through the hide. * * * It has been stated 

 by various authorities that the young grub emerging from the shell bored its way 

 through the skin until it reached the subcutaneous tissue, and thus made its chan- 

 nel. From circumstantial evidence I believe that the embryos are licked by the cattle 

 and swallowed, or lodged in the back of the mouth or oesophagus. This theory is 

 based on the appearance of the cattle grubs in the walls of the oesophagus in No- 

 vember, long before they are found iu the backs of cattle in this locality. Later, 

 about Christmas time, the grubs appear suddenly, and in full force under the skin 

 of the back. At their first appearance under the skin they are as large as those 

 found in the oesophagus at that time, and differ in nowise from them. By the latter 

 part of January or early in February all have disappeared from the oesophagus, to- 



