﻿42 BULLETI3sr 136&, tJ. S. DEPARTMENT OF AGRlCtTLTUEE 



number depends to some extent upon whether the fiy is disturbed 

 during the process of oviposition and also upon the length of the 

 hair. In the case of H. hovis the eggs are always deposited singly 

 on the hair. 



DISTRIBUTION OF EGGS ON HOST 



n. lineatum shows a marked tendency to oviposit on the heels of 

 cattle which are standing, the favorite place apparently being the 

 short hair overhanging the rear of the hoof and between the hoof 

 line and the dewclaw^s. Many eggs, however, are deposited higher 

 on the legs in the region of the hocks and a few above the hock line. 

 Some eggs are also deposited on the belly, flanks, and forelegs, and 

 occasionally on the sides, shoulders, and neck. In practically all of 

 the writers' observations of depositions on cattle which are not lying 

 down, it seems evident that many of the eggs deposited elsewhere 

 than on the heels are laid after the fly has been disturbed by the 

 actions of the host. Many eggs are also deposited along the es- 

 cutcheon, on the outside of the thighs, on the tail, and on the base of 

 the udder, and some along the side and on the forelegs in the region 

 of the elbow joint. Infestations in these regions are especially com- 

 mon among quiet stock, oviposition taking place while they are 

 lying down. In one instance over 200 fresh eggs were found attached 

 to the hair on an area not over 2 inches square just behind the upper 

 end of the scapula. The writers' observations on flies in nature and 

 upon those placed on hosts in captivity indicate that they prefer the 

 short, comparatively coarse hairs to the long, dense, silky ones. 



FI. hovis also prefers the heel or lower leg for a place of attach- 

 ment for its eggs, but since this species frightens the animals much 

 more, and since the flies continue to follow the cattle, depositing eggs 

 while pursuing the rapidly running animals, a much larger per- 

 centage of eggs is deposited higher on the legs, especially in the 

 region of the thighs and on the rump. Although a considerable 

 number of eggs are laid on other parts of the body, especially along 

 the sides, they tend to be concentrated on the hind quarters. 



METHOD OF ATTACHMENT OF EGGS 



As has been indicated under its description, the egg is provided 

 with a definite attachment area or clamp. In addition to the place- 

 ment of the clamp around the hair, each egg appears to be provided 

 with a cement which when dry firmly glues it to the hair. Eggs 

 have been observed to remain attached on the host for several weeks, 

 sometimes the distal end gradually breaking away so as to leave 

 only a portion of the shell. As shedding of the winter coat usually 

 takes place about the time the eggs are deposited, many of them 

 are shed off and perish before they have had an opportunity to 

 hatch. 



The eggs are nearly always attached very close to the skin, and 

 this renders them inconspicuous, as they are usually covered by the 

 overhanging hair. This is particularly true of H. hovis. 



INCUBATION 



The incubation period of H. lin£atu?)i, as observed in many lots 

 of eggs kept under varying conditions, was found to range from 



