62 PARASITES OF THE DOMESTIC ANIMALS 



seeing that they cannot feed. This hfe history apphes to Agassiz, 

 British Cohunbia; doubtless in other countries variations will be noticed, 

 but the period spent by the larvae within the host must be of the same 

 duration, seeing that animals' temperatures are the same the world over." 



Effect. — Cattle seem to be much annoyed by the attacks of these 

 flies in depositing their eggs, and in the endeavor to escape will often 

 enter mire holes or injure themselves in other ways. Probably the most 

 important damage from the insect is that to hides, these being dis- 

 counted from twenty-five to fifty per cent, according to the number of 

 punctures by the grubs. 



Treatment. — Treatment is best applied in the months of January 

 and February when the grubs have become sufficiently developed that 

 the small tumors in which they are lodged may be felt by running the 

 hand along the back of the animal. The application at this time of a 

 little kerosene or mercurial ointment to the summit of the swelling will 

 destroy the grub. By March the tumors may be distinctly seen as 

 prominent lumps upon the skin of the back. The orifice at the summit is 

 now large enough to permit of the forcing out of the grub by careful 

 pressure. Grubs thus removed should be at once destroyed to prevent 

 the possibility of their finding favorable conditions for development 

 into the adult fly. 



QllsTRUS Ovis 



The sheep botfly (Fig. 33, 1 and 2) .— CEstridce (p. 53). About one- 

 half an inch in length ; yellowish-gray color ; slightly hairy. The abdomen 

 is spotted with white and yellow; posterior portion covered with fine 

 hairs. The wings are transparent. 



Occurrence and Life History. — This species is of world-wide dis- 

 tribution, and is the most important insect pest with which sheepmen 

 have to deal. The flies make their appearance with the coming of warm 

 weather from early June to July, like other (Estridae, flying on bright 

 and warm days and ceasing their activities about the month of October. 

 The female, which is difficult to observe owing to its small size and rapid 

 flight, deposits living larvae in the nostrils of the sheep. At this time 

 the larva is creamy-white in color and about one-sixteenth of an inch 

 in length (Fig. 33, 6). Later it becomes darker, and at maturitj^ reaches 

 a length of about three-quarters of an inch (Fig. 33, 4 and 5). Upon the 

 cephalic segment there are two hooklets the points of which are curved 

 downward and backward. With the aid of these the larva at once pro- 

 ceeds to work its way upward through the nasal passages until it reaches 

 the frontal sinuses where it attaches by its hooklets to the lining mem- 

 brane. Here it feeds upon mucus and serous exudate induced by the 

 irritation of its presence. 



The larva remains in this location about ten months, at the end 



