162 INSECTS AND MAN 



life-cycle, the chances of its reaching maturity are much 

 lessened, for at any stage starvation may be the result 

 of the non-appearance of the host within a reasonable 

 period. To some extent this disadvantage is overcome 

 by the superior powers of resistance possessed by all ticks 

 belonging to this class ; they are less affected by heat and 

 cold than other ticks, and they are able to withstand pro- 

 longed fasting. 



The majority of ticks favour certain hosts, hence the 

 popular names, sheep tick, dog tick, etc. ; they may, however, 

 attach to other hosts, on occasion ; in this event, one animal 

 is called the usual and the other the accidental host. A 

 very curious example of this host relationship is exhibited 

 by the Senegal tick, Hyalomma cegyptium. In its larval 

 stage it attaches to fowls and cannot be made to feed upon 

 any mammal ; while attached to its avian host, it under- 

 goes its first moult. The second moult takes place while 

 unattached to any host; then, when the adult stage is 

 reached, the tick will attach to almost any mammal, except 

 the dog. 



As we have already remarked, all ticks must find hosts 

 and attach to them at least once, sometimes as often as 

 four times, during their life-cycle. The result is that they 

 show very special adaptation of structure and function 

 for attachment. In the family Ixodidce, for instance, the 

 larvae or " seed ticks " use their front legs in a very peculiar 

 manner standing erect, on some elevated support, they 

 wave their anterior legs in the air whenever a likely host 

 approaches, and, when once these legs come in contact with 

 anything of a solid nature, they cling most tenaciously, 

 as anyone may prove by passing a finger over a cluster 

 of "seed ticks." In this case, the larval legs are used 

 solely as sentinels and grappling irons for attachment. 



Structure may also be adapted for protection, as ex- 

 emplified, to some extent, in the sub-family Ixodince, or 

 hard ticks, which have mouth parts of such formidable 



