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. 15G). 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 

 apparatus consists of a sys- 

 tem of tracheae which open 

 by a pair of spiracles in the 

 vicinity of the fourth pair 

 of legs. The shape of the 

 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 ])irds 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 th(^ immature forms. 





Fig. 152. Hypostomes of ticks; A, ear 

 tick, Otiobius (or Ornithodorus) inegnini, 

 nymph; B, Argas persicua, adult; C, Ixodes 

 ricinus, adult female; D, same, male; E, 

 Ixodes vespertilionis, adult female; F, same, 

 male; G, Ornithodorus mouhata, nymph; 77, 

 Ornithodorus savignyi, adult. {A, after Sal- 

 mon and Stiles; others after Nuttall.) 



