CHAPTER XXX 



The Biologies and Habits of Ticks ^ 

 F. C. Bishopp 



The importance of ticks as vectors of disease and as simple parasites 

 has directed the attention of many workers to this group. Although the 

 superfamily Ixodoidea, which comprises the ticks, is comparatively small, 

 the species numbering about 300, the life-histories and habits of the 

 species are quite varied. Many forms exhibit a close correlation between 

 their habits and habits of their hosts. There is often also a marked rela- 

 tionship between seasonal and climatic conditions and the presence and 

 abundance of different species. 



Knowing the intimate interdependency between ticks, their hosts, and 

 several serious diseases of man and animals, and also considering the 

 fact that all important control measures are based upon the life histories 

 of the species concerned, we cannot too strongly emphasize the need 

 of a thorough knowledge of host relations, distribution, and life histories 

 of the more important species. 



Stages in the Life of Ticks. — There are two distinct families com- 

 prising the ticks. One of these, known as the Argasidae, may be recog- 

 nized by the absence of any highly chitinized parts, while the other, the 

 Ixodidae, is supplied with a definite, highly chitinized scutum or shield (on 

 the dorsum anteriorly), and highly chitinized legs and other parts. 



There are usually four distinct stages in the life of all ticks. The 

 ^gg, which is more or less oval in shape and usually brown in color, the 

 larva or six-legged stage, the n3'mph or second stage (with eight legs), 

 and the adult tick in which the sexes are well defined. In several species 

 we have a second or even third nymphal stage. In tlie Ixodidae the males 

 and females are usually readily distinguished in the unengorged state. 

 The female has a chitinized shield covering almost the entire dorsal side. 

 In this group of ticks the female is the only one which becomes greatly 

 distended with blood, and being quite conspicuous when engorged, is the 

 form usually observed by the layman. In practically all the species the 

 males attach and imbibe some blood, but do not become greatly swollen. 



Habits. — There are certain general habits which are peculiar to the 

 two families of ticks. Most species in the family Argasidae remain free 



* Tliis lecture was prepared for this edition only. 



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