THE TICKS 



141 



Ear Tick, Argasidse (p. 139). — The body is oval, broader anteriorly than 

 posteriorly. The female is 5-6 mm. (3^ of an inch) in length and about 

 3 mm. {^/s of an inch) in breadth. The nymphs are co^'ered with nu- 

 merous spines, a fact which has given to this species the common name 

 "spinose ear tick." 



Occurrence and Habits. — This tick occurs in the ears of horses of 

 Mexico and the Southwestern States. Its attack is not confined to 

 horses and mules; it also attacks the ears of cattle and occasionally other 

 domestic animals and man. The larval ticks reach the head of the graz- 

 ing host animal from weeds or other vegetation upon which they have 

 crawled immediately after 

 hatching. Having gained en- 

 trance to the ear, they attach 

 deeply in the folds where they 

 feed for about five days. 

 They then molt and, as 

 nymphs with spinose bodies, 

 continue to infest the ear and 

 feed for several weeks. The 

 nymphs then leave the host, 

 again molt, and becoming 

 unspined adults, the females 

 are fertilized and soon begin 

 depositing their eggs. 



Effect. — In their attach- 

 ment to the lining of the 

 conchse the spinose ticks 

 cause much' irritation which 

 the animal indicates by shak- 

 ing its head, or it may be 

 wrought up to a high degree of nervous excitement. 



Fig. 80. — Otobius megnini: dorsal and ventral 

 view of nymphal form, with details (after Osborn, 

 from Marx, Bull. No. 5, Bureau of Entomology, 

 U. S. Dept. of Agr.). 



The ticks are said 

 to be responsible for much deafness among domestic animals, and, 

 especially among young animals, they are considered as a cause of se- 

 rious illness and even death. 



Treatment. — Good results have been obtained by flooding the ear 

 with carboKzed oil. This closes the breathing apertures of the ticks and 

 causes them to release their attachment, after which they may be re- 

 moved with a cotton swab or forceps and destroyed. 



Family II. IxoDiDiE 



Ixodoidea (p. 139). — The most prominent differential character by 

 which these ticks may be distinguished from those of the family Ar- 

 gasidae is the presence of a scutum, located immediately posterior to 



