70 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
place among reared specimens. Among a large number of adults | 
of H. bovis which emerged early in the morning and were kept in — 
lantern globes, many pairs were observed in copula about 10 a. m.. 
as the temperature rose. The duration of the act ranged from two 
to two and one-half minutes. 
OVIPOSITION 
Reference has been made already to an instance of a fly begin- | 
ning oviposition within about an hour of the time she emerged. 
The writers’ observations in the field indicate that if favorable 
weather conditions prevail oviposition usually begins on the same 
day the adults emerge. It — 
also appears that with flies — 
in the field and with those 
captured and placed on ex- | 
perimental animals the ma- 
jority of the eggs deposited | 
by an individual are laid 
during a single day. In| 
several instances flies de- — 
posited a large number of 
eges during one day and a_ 
moderate number during — 
the second day, but in no 
case have specimens ovi-— 
posited during three suc-_ 
cessive days. | 
As has been pointed out 
by Hadwen and other au- 
thors, the methods of ovi- 
position are very different — 
in H. lineatum and A. 
bovis. The former attacks 
more stealthily than the 
latter, and several eggs are 
usually placed on a single — 
Fic. 32.—Heel fly (Hypoderma lineatum) oviposit- hair, while with Z. bovis | 
ne ane Wag he as Roe “the eggs are laid singly. — 
This difference in the action” 
of the flies during their oviposition is intimately associated with the 
fright produced among cattle, as will be discussed later. 
In the field when cattle come in the vicinity of a resting female 
of H. lineatum the insect is observed to approach them on the wing 
usually alighting on the ground close to an animal and frequently 
approaching the hind legs of the host by a series of short flights 
which resemble jumps. She sometimes lights directly on the heel,” 
usually below the dewclaws, and immediately begins to extend the 
ovipositor, g rasping the hair and cementing on her eggs (fig. 32)._ 
In other instances if the animal is not moving she may come close 
to the heel of the host, turn around, and back up to the rear of — 
the hoof with the ovipositor extended. In this way the short hairs — 
between the hoofs are reached and the eggs are placed in position 
