vidiials, even thorigh they stcrvive long periods without food. Their 

 extended life cycle subjects them to many adversities depending on 

 season and the peregrinations of their hosts. The requirement of 

 two or more kinds of hosts, often with divergent habits, limits 

 their distribution to certain faunal areas. The comparatively- 

 large size of females makes them subject to injury and tempting 

 food for predatory arthropods and vertebrates. Certain pathogenic 

 organisms, fungi, and hymenopterous pairasites kill them. Ticks 

 have little protection against an enemy except their ease of coru 

 cealment. They are particularly susceptible to attack during the 

 lethargic premolting and the weak postmolting period. 



On the other hand, many biological features enable ticks to 

 survive especially well. They lay numerous eggs and withstand a 

 comparatively wide temperature and humidity range with greater 

 ease than many other arthropods. They survive for months or years 

 without food and often gain considerable protection from the con- 

 cealed places in which they feed on the host. They frequently are 

 offered a wide choice of appropriate hosts. Should they annoy the 

 host, the animal is usually powerless to rid itself of the para- 

 site. Ticks* slow metabolic rate has certain advantages and the 

 leathery, usually inconspicuous, integument offers some protection 

 from living enemies, water, and chemicals. Parthenogenesis, pos- 

 sibly a common occurrence though not well studied, may aid sur- 

 vival. 



The genus Ixodes , as a biological unit, shows much divergence 

 from the usual patterns of ixodids. The biology of this genus 

 must be considered independently but in relation to other genera. 

 Review summaries frequently leave the student with the impression 

 that the unique biological characters of Ixodes ticks are also 

 characteristic of other ixodid genera. 



The degree of host specificity in ixodid ticks varies from 

 genus to genus or within certain subgroups of various genera. 

 Generalizations on this point should be very carefully qualified. 



Eggs are laid only once; promiscuously; at one time and place; 

 gind are always niimerous, sometimes numbering over 10,000, Eggs 

 hatch in from two weeks to several months, depending mostly on 

 climatic factors. 



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