﻿62 



BULLETIN 1369, U. S. DEPAKTMENT OF AGEICULTUEE 



THE METHOD OF EGRESS OF GRUBS FROM BACKS OF CATTLE 



When the fifth-stage larvse complete their growth they become 

 more active and the posterior segments are extended' and forced 

 into the openings through the skin and then quickly withdrawn. 

 With this action the sides of the holes are cleaned of the rim of 

 exudate and more or less covered with the pus forced up by the 

 larvse. When the actual process of emergence begins the posterior 

 segments are forced into the aperture and the larvae slowly work 

 their way out by expansion and contraction of the body rings. 

 The actual process of emergence of the gi'ubs takes from one to 



f^To o-d^ qL/a^ x^TT/ y^-fy*^ y^-y 7-"^ O- 3 ^_>* >*_.^- ^ -!=•- -^ "> 



so\ 



z-s &s S-/0 /^-// //-/z /^-/ /-^ ^-3 s--^ ^-^ s^s e-z 



Fig. 29. — Diagram showing hours when larvae of Hypoderma lineatum emerge from 



the host for pupation 



three minutes, but the preparatory activities may be begun several 

 hours before the grubs make a serious attempt to escape. 



TIME OF EMERGING FROM HOST 



With H. lineatum fairh^ accurate observations have been made 

 on the time of day when 181 warbles emerged from the host, and 

 less accurate observations on 211 others. (Haser {29) pointed out 

 that he observed in Germany a large percentage of warbles dropped 

 in the early morning hours, the percentage being from 49.4 to 68.2 

 between the hours of 5 and 7 a. m. The writers' observations do 

 not agree closely with his in this respect, for, as is shown on the 

 accompanying cliagram (fig. 29), the largest number dropped in 

 the middle of the forenoon from 8 to 10 a. m., and the emergence 



