366 TICKS 



come ill-tempered and emaciated. Children sometimes suffer 

 a great deal from their attacks, and have difficulty in dislodging 

 the invaders from their ears. This can readily be done, however, 

 by pouring olive oil or some other harmless oil into the ears. 



Although there are a large number of species of the family 

 Ixodidae which may attack man, they do not as a rule prove as 

 great pests or produce as severe bites as some of the Argasidae. 

 The characteristics of some of the principal genera are given in 



FIG. 161. Diagrams of rostra or capitula of important genera of Ixodid ticks, 

 useful in identification. (After Nuttall.) 



With long rostrum Other characteristics 



A, Ixodes Anal, groove in front of anus, no eyes, 



no festoons. 



B, Hyalomma eyes present, festoons present. 



C, Amblyomma eyes present, festoons present, ornate. 



or 

 Aponomma eyes absent, festoons present, ornate. 



With short rostrum 



D, Hcemaphysalis eyes absent. 



E, Margaropus circular spiracles. 



F, Rhipicephalus comma-shaped spiracles. 



G, Dermacentor eyes present, ornate. 



Fig. 161 and accompanying table. Only a few species need 

 special mention here. Dermacentor venustus is, of course, of 

 preeminent importance on account of its role as a transmitter 

 of spotted fever and in producing tick paralysis. D. occidentalis, 

 the " wood tick " of the Pacific slope of the United States, is 

 another member of the genus which very commonly attacks man ; 

 its bites are particularly likely to cause ugly ulcerating sores. 

 Experimentally, as said before, it has been shown to be capable of 

 transmitting spotted fever, and it would probably act as an effi- 



