2 | a 
THE CATTLE GRUBS OR OX WARBLES 25 
sore and tender from the penetration of the larve, the animals are 
more easily aroused and terrorized. 
After a herd has been attacked for a few days in spring, it is only 
necessary to have a single fly begin to oviposit on an animal in order 
to start the whole herd from pasture to some protected place. When 
water is at hand it furnishes the preferred and most effective pro- 
ild dash for pro- 
king w 
d, calves crowding into shade to escape heel- 
is ma 
° 
? 
lm to escape heel-fly attack 
‘ 
c 
attacked by adult Hypoderma: a, Cow showing attitude assumed when heel 
© 
« 
eatum) first attacks; 6, heifer attacked by Hypoderma bov 
stre 
in 
ing 
and 
€ 
re 
of eattle when 
Actions 
c, cows st 
(Hypoderma lin 
9 
5. 
tection 
fly attack 
fly 
lia. 
‘tection. Animals have been observed to remain standing in the 
water practically all day when adults of H. lineatum were numerous, 
and apparently without ever being molested by flies (fig. 5, c), even 
though the water was not more than a few inches deep. Shade offers 
‘considerable protection and is usually sought in the absence of water. 
(Fig. d,d.) H. bovis is less easily repelled either by water or shade 
