62 BULLETIN 1368, U. S. DEPARTMENT OF AGRICULTURE 
THE METHOD OF EGRESS OF GRUBS FROM BACKS OF CATTLE 
When the fifth-stage larve 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into the openings through the skin and then quickly withdrawn.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 
_larve. When the actual process of emergence begins the posterior 
segments are forced into the aperture and the larve slowly work - 
their way out by expansion and contraction of the body rings. — 
The actual process of emergence of the grubs takes from one to 
HIOWR: OF EIIERGENWCE OF LARLAE FRO/T HOST 
tS SS LS Ee) 
FE. GF GIO JOM PISEAEVAEL ESB FF LES FOO 
SS SS Se Se 
La 
FE 
FE | 
44 
FZ 
NU/IIBER OF LARVAE 
ONAAHISTISSNHUITENRRGS 
Fic. 29.—Diagram showing hours when larve 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 fairly accurate observations have been made 
on the time of day when 181 warbles emerged from the host, and 
less accurate observations on 211 others. Glaser (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 diagram (fig. 29), the largest number dropped in 
the middle of the forenoon from 8 to 10 a. m., and the emergence 
