58 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
vary considerably, but they are usually much larger after the molt 
to the fifth stage, and measure from 3 to 4.5 millimeters in diameter 
(fig. 27). It is seldom that any scabbing or other obstruction is 
found in the aperture over a fifth-stage larva. There is usually to 
Fic. 27.—Close view of portion of cow’s back infested with cattle grubs.. Hair is 
clipped from around holes 
be seen a rim of exudate, part of which is considered to be excrement, 
around the outside edge of each hole. 
The position of the larva is similar to that in the fourth stage. 
The posterior end of the segments is bent slightly so as to bring the 
