ANIMAL, PARASITES OF CATTLE. 511 



to crusli all grubs removed, so as to prevent the possibility of their 

 further development and transformation into flies. (In order that 

 none may escape it is advisable to examine the cattle every two 

 weeks during the late winter and spring, at each examination remov- 

 ing the grubs which have developed sufficiently to cause perceptible 

 swellings. 



Another method of treatment is to force grease or oil into the open- 

 ings of the warbles, which kills the grubs. This method is less cer- 

 tain than that of removing the grubs, and has the further objection 

 that the dead grubs remain beneath the skin. 

 vCattle may be treated during the summer with fly repellents 

 (p. 502) to keep off the warble flies. The efficacy of repellents against 

 these flies is probably, however, not very great. 



In localities where the character of the cattle industry is such as 

 to render practicable the systematic examination of cattle and the 

 removal of the grubs — that is, where the herds are comparatively 

 small and subject to the close supervision of the owners — it is pos- 

 sible, by the exercise of a little care and with very little effort on the 

 part of the cattle owners, provided they work together, each doing 

 his share by seeing to the removal of grubs from his own cattle, so 

 that as few as possible survive to transform into flies, to reduce the 

 number of grubs within one or two seasons almost, if not entirely, to 

 the point of extinction. 



Investigations not yet completed indicate that grub eradication 

 may sometimes be accomplished by the use of arsenical dips, which 

 are extensively used at the present time for destroying cattle ticks. 

 (See p. 497.) It is possible that the destructive action of arsenical 

 dips upon warbles is more or less dependent upon the fact that 

 arsenic is stored up in small quantities in and upon the skin of cattle 

 that are repeatedly dipped in arsenical dips. The arsenical dip ap- 

 pears to act, not upon the well-developed grub beneath the skin, but 

 upon the eggs or the newly hatched larvae, probably the latter. Ac- 

 cordingly the dipping of cattle to destroy grubs should be carried 

 out during the fly season and repeated treatments should be given 

 every two or three weeks, as in dipping cattle to eradicate ticks. 



Cattle in the United States are commonly infested with three 

 species of lice, two of them sucking lice {Hxmatopinus eurysternus, 

 the short-nosed cattle louse, and Linognathus mtuli, the long-nosed 

 cattle louse), commonly known as blue lice, and one biting louse 

 ( Trichodectes scalaris) , commonly known as the red louse. 



1 For further information see Farmers' Bulletin 90S. 



