316 



SUMMARY AND CONCLUSIONS. 



The facts here recorded, iu the light of the hitherto miiversally ac- 

 cepted views in reference to the life-history of the Ox Bot, are ex- 

 tremely interesting. They may be summarized as follows : 



In Korth America, so far as we yet know, Sypo- 

 derma hovis does not occur. Considering the fre- 

 quency with which cattle have been imported into 

 this country from abroad this fact seems almost in- 

 credible, yet until the species is observed and recorded 

 FiG.5i.—Hypodermabo- ^^ must cousider its prcscnce in America as merely 



VIS: head of female fly 



from the front — on- conjcctural. The American Ox Warblc, in cvcry casB 

 larged (after Brauei). g^ f.^y obscrvcd, is the larva of Hypoderma lineata. 

 This species has come to be known, esi)ecially through the South and 

 Southwest, as the Heel Fly, on account of the habit which the female 

 has of frequenting the legs of animals for pur- 

 poses of oviposition. While tlie eggs are laid 

 on other parts of the body that may be reached 

 by the tongue, the species shows quite a strong 

 tendency to select the flanks and legs around 

 the heels, and the habit, almost everywhere ob- ^ "/ 



served, that cattle have of seeking to protect t;-,^ =r ^ , , ■ 



' '^ i Fig. 55. — Hypoderiiia hovis: a, 



their legs by running into water during the bot- puparium, from side; 6, same, 

 fly season finds its explanation in these facts, f'-om-'^bove, showing exit hole 



"^ of adult; c, cap which splits 



The eggs are attached firmly, by a strong cleft, off to aiiow the aduit to issue- 

 in rows of from five to ten or more, to the hairs, "aturai size (after ciart). 



When the cattle lick themselves, the young larvse are taken into the 

 mouth, as, under pressure and moisture, the egg readily splits at its 

 anterior end and releases the young larva, which is already well de- 

 veloped when the egg is laid. Doubtless quite frequently the eggs 

 with the contained larvae are taken with the hair in this licking, but in 

 either event the larva in leaving the egg is armed with many minute 

 spines, which permit it to adhere to and to penetrate the walls of the 

 esophagus. Here it soon molts and takes on the second of smooth 

 stage, which for eight or nine months wanders slowly in the tissues of 

 its host. The slow movement and the little nourishment taken reduce 

 the inflammation and irritation to a minimum; in fact, the most re- 

 markable thing in the life-history of this larva is the long period of la- 

 tency and the slight development that takes place during the summer 

 and autumn months. During the late winter the larva reaches a point 

 beneath the skin in the region of the back and penetrates the skin, 

 anal end first as Dr. Curtice believes, and as seems most probable. 

 Here it molts a second time and reassumes its spinous character, pro- 

 ducing more or less inflammation and developing rapidly with its en- 

 larged spiracles fitted for more perfect breathing. The third molt soon 

 follows, and we get the more strongly spined grub, with its still larger 

 spiracles, which lives in the swellings or sacs so mcII knoMU to stock- 

 men. It finally works its way out, droi)s to the ground, which it enters. 



