ENTOMOLOGY

CHAPTER XXXThe Biologies and Habits of Ticks 1F. C. BiahoppThe importance of ticks as vectors of disease and as simple parasiteshas directed the attention of many workers to this group. Although thesuperfamily Ixodoidea, which comprises the ticks, is comparatively small,the species numbering about 300, the life-histories and habits of thespecies arc quite varied. Many forms exhibit a close correlation betweentheir habits and habits of their hosts. There is often also a marked relationshipbetween seasonal and climatic conditions and the presence andabundance of different species.Knowing the intimate interdependency between ticks, their hosts, andseveral serious diseases of man and animals, and also considering thefact that all important control measures are based upon the life historiesof the species concerned, we cannot too strongly emphasize the needof a thorough knowledge of host relations, distribution, and life historiesof the more important species.Stages in the Life of Ticks.-There are two distinct families comprisingthe ticks. One of these, known a,s the Argasidre, may be recognizedby the absence of any highly chitinized parts, while the other, theIxodidae, is supplied with a definite, highly chitinized scutum or shield (onthe dorsum anteriorly), and highly chitinized legs and other parts.There are usually four distinct stages in the life of all ticks. Theegg, which is more or less oval in shape and usually brown in color, thelarva or six-legged stage, the nymph or second stage (with eight legs),and the adult tick in which the sexes are well defined. In several specieswe have a second or even third nymphal stage. In the Ixodidae the malesand 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 greatlydistended with blood, and being quite conspicuous when engorged, is theform usually observed by the layman. In practically all the species themales attach and imbibe some blood, but do not become greatly swollen.Habita.-There are certain general habits which are peculiar to thetwo families of ticks. Most species in the family Argasidae remain free1 This lecture was prepared for this edition only.430