THE CATTLE GRUBS OR OX WARBLES 71 
while the fly remains on the ground. When the animal moves, the 
fly usually follows, flying behind close to the ground, and when the 
opportunity offers she may ahght on the host, commonly on the 
hind legs below the hock. Under such conditions the animal is ' 
usually aware of the presence of the fly and often kicks at it, fre- 
quently knocking it to the ground, in which case it usually arises 
promptly and starts again after the host. With animals disturbed ° 
in this way the fly is more lkely to attack higher on the lees and 
not infrequently on the sides, especially in the region of the flank 
or on the forelegs or shoulders. | 
In many instances the writers have observed females of ZZ. Tene 
twm to oviposit on cattle while they were lying down. When not 
disturbed the fly usually deposits a series of eggs, possibly 50 to 
60, in rapid succession and then rests for a minute or two. Some- 
times she moves slightly to a new position and then repeats the 
operation. 
Flies of H. lineatum captured by means of a net. while attacking 
cattle in nature are readily induced to oviposit on experimental 
animals kept under control; in fact, this was the method followed 
in obtaining eggs with which to infest experimental animals and 
for other purposes. After the flies were captured they were usually 
placed in small tubes or jars and brought immediately to the 
laboratory and placed upon experimental hosts. To accomplish this 
the female was usually placed in a glass vial with the open end 
placed against the host. Usually as soon as the fly comes in. con- 
tact with the hair of the animal she begins extending the ovipositor 
and starts laying eggs. After she has once begun itis often unneces- 
sary to keep the restraining vial over her. 
HZ. bovis attacks the animals viciously, usually approaching them 
about the height of the hock, and very seldom lights on the ground. 
On account of its more ‘persistent and ferocious attack the animals 
are put to flight with the first period of oviposition. The fly strikes 
the animal a number of times in rapid succession, cementing an 
egg on, a hair in nearly every instance. After a number of these 
strikes at the animal the fly may leave for a few minutes and then 
return. and repeat the process as persistently as before. Frequently 
when the host is active the fly may follow it around a small pas-. 
ture, attacking repeatedly when it catches up to the fleeing animal. 
Great difficulty was experienced in getting females of /7. bovis 
to deposit. eggs after they had been captured. Hawden’s reports 
indicate that he had no difficulty in getting females caught while 
Ovipositing in nature to deposit under an insect. net. held to a bovine 
or when released near a tethered animal. In Illinois and New 
York, however, a number of flies captured in the field by the writers 
and applied 1 in various ways to hosts under control gave very dis: 
couraging results. Only a few ego's were secured and these for the 
most part were dropped free in the hair. 
During the summer of 1922 a large number of flies ae both sexes 
of H. bovis were reared at Middletown, N. Y., and many attempts 
were made to secure eges from them. Although they mated freely, 
as has been stated, they ‘persistently refused to oviposit. Some were 
kept in glass containers held against a calf; others were placed in 
small screen cages attached to the host; and still others were liberated 
