4 FARMERS BULLETIN 798. 



Many of the farm flocks of the United States harbor sheep ticks and 

 in some cases they are present in sufficient numbers to cause con- 

 siderable damage to such flocks. This is especially ti'ue where open- 

 fleece sheep are kept. 



The sheep tick obtains its food by puncturing the skin of the sheep 

 with its lance-like proboscis or sucking tube and feeding on the 

 blood and lymph. The irritation thus caused is very great, especially 

 in the case of lambs that are infested heavily, and while the quantity 

 of blood draAvn by one tick in -24 hours is small, the total amount 

 taken by a large number of ticks is considerable and the drain con- 

 stant. The irritation caused by the ticks makes the sheep restless so 

 that they do not feed well, and in consequence, they do not grow and 

 fatten as rapidly as when free from ticks. Thus a loss is caused by 

 shrinkage in weight and a general unthrifty condition of infested 

 flocks, with a consequent lowering of the vitality and a reduction in 

 the resisting power of the animals. These conditions not only help 

 to reduce the market value of the sheep but also tend to reduce wool 

 growth, although being a bloodsucker, the tick does not feed on 

 the yolk of the wool or directly injure the fibers to any great extent. 



During the course of the investigations conducted by the Bureau 

 of Animal Industry bearing on the problems of eradication, estimates 

 of the average annual losses caused by sheep ticks were submitted 

 by a large number of sheep owners in Utah. According to these 

 estimates, the average annual losses are 25 cents per head for lambs 

 and 20 cents per head for ewes in infested flocks. These figures are 

 undoubtedly very conservative, as in estimating losses caused by 

 parasites the indirect losses are seldom taken into consideration. 

 Any factor operating to lower the vitality and resisting powers of 

 domestic animals usually causes indirectly a considerable death loss 

 during unfavorable seasons. The old saying, '' Poverty breeds 

 parasites,^" might with at least equal truth be read the opposite way, 

 " Parasites breed poverty." 



LIFE HISTORY. 



The sheep tick, being a wingless fly, is in no way directly related 

 to the true ticks. A true tick in the adult stage has 8 legs, while 

 the so-called sheep tick has only 6 legs and in general form and struc- 

 ture is entirely diflerent. (See fig. 1.)^ Like other insects, sheep 

 ticks vary in size, but the average length of adult females is about 

 one-quarter of an inch. The life cycle of the sheep tick is divided 

 into four natural stages or divisions, namely, the egg, the larva, the 

 pupa, and the adult or sexually mature insect. 



1 Figures 1 to 8 are from photographs by Dr. W. T. Huffman, and the picture on the 

 title page is from a photograph by Dr. George A. Lipp. 



