354 



TICKS 



Most ticks have a little shield or " scutum " on the dorsal sur- 

 face, quite small in the females, but nearly or quite covering the 

 back in the males (Fig. 156). Attached to it in front is a little 

 triangular piece, the capitulum or " head " which bears the 

 mouthparts (Fig. 150). The latter consist of a quite formidable 

 piercing organ, the hypostome, a pair of chelicerae or mandibles 

 which are armed with hooks (Fig. 151), and a pair of blunt palpi 

 which are probably tactile in function. The hypostome is a 

 rasplike structure, beset with row after row of recurved teeth 

 (Fig. 152). So firmly do these hold in the flesh into which the 



proboscis is inserted that 

 forcible removal of a tick 

 often results in the tearing 

 off of the body from the 

 capitulum which remains at- 

 tached to the host. Like 

 other Arachnida, ticks have 

 four pairs of legs. These 

 are quite conspicuous when 

 the body is empty but are 

 hardly noticeable after en- 

 gorgement. The breathing 

 - ^- H y post mes , f tic , ks; f f ar apparatus consists of a sys- 



tick, Otwbius (or Ornithodorus) megmm, 



nymph; B, Argas persicus, adult; C, Ixodes tem of tracheae which Open 



ricinus, adult female; D same, male; E, by ft pair Q f sp i rac l es i n t he 



Ixodes vespertilioms, adult female; F, same, **. 



male; G, Ornithodorus moubata, nymph; H, Vicinity of the fourth pair 



Ornithodorus :savignyi, adult (A L, after Sal- f j The gh f th 



mon and Stiles; others after Nuttall.) r 



plates which cover the spir- 

 acles are sometimes used in distinguishing species. The ventral 

 surface has two openings, the genital pore just back of the pro- 

 boscis, and the anus some distance from the posterior end of the 

 body (Fig. 154). 



Habits and Life History. All ticks are parasitic during some 

 part of their lives. The majority of them infest mammals, 

 though many species attack birds and some are found on cold- 

 blooded animals. A very decided host preference is shown by 

 some species, whereas others appear to be equally content with 

 any warm-blooded animal which comes their way. In many 

 species the hosts or parts of hosts selected by the adults are not 

 the same as those selected by the immature forms. 



