Larvae are active and sometimes are easily visible as hun- 

 dreds or thousands of them rest on grass awaiting a host. Larvae 

 often parasitize small mammals, birds, and reptiles, sometimes in 

 their nests or dens. Only a few kinds choose larger animals for 

 hosts. Thickness of the host skin is possibly an importeint fac- 

 tor in restricting larvae to smaller animals. Larvae seldom feed 

 within a week after hatching. 



After sorae days of feeding, larvae molt to nymphs on the 

 same host (two-host type of life cycle), or drop from the host 

 and some time later molt to nymphs (three-host type of life 

 cycle) on the ground. Exceptions are the single-host boophilid 

 ticks (and a few others) that molt and remain on a single host 

 during their lifetime. Nymphs that have molted on the ground 

 seek a new host, sometimes the same type they fed on as larvae 

 but, more commonly, animals similar to hosts preferred by adults. 

 After several days of feeding, nymphs drop to the ground; be- 

 come quiescent for a time, then molt to adults. There is only 

 a single instar in the nymphal stage (see footnote, page 141 ). 

 Some species may undergo one or another of these variations in 

 life cycle, depending on climatic, seasonal, or nutritional fac- 

 tors, most of which are still poorly evaluated. 



There is evidence that in certain three-host species (in 

 which larvae characteristically feed on small mammals) larvae 

 that feed on a somewhat larger animal, such as a hare, may re- 

 main on the host, molt to nymphs, and continue feeding. They 

 drop from the larval- nymphal host only before molting to the 

 adult sta^e. 



Nymphs and females become tremendously engorged and new 

 cuticle is developed during the rather slow feeding process in 

 order to accommodate the huge volume of blood ingested. Males 

 become only slightly distended if at all, apparently, as in 

 argasid ticks, by stretching the integument althotigh they may 

 remain in a feeding position for months, even after the slaugh- 

 tered host's skin has been removed. 



As reservoirs of a great variety of pathogenic organisms, 

 ixodids are pre-eminently important, whether they act as vectors 

 or not. As vectors, they transmit a greater variety of organisms 



- 203 - 



