IV 

 INSECT ENEMIES OF LIVE STOCK 



TICKS AND DISEASE 



THE ticks are of primary importance as vectors of disease ; 

 no less than ten distinct human and animal diseases are 

 known to be transmitted by these creatures. Apart from 

 their disease-carrying propensities, ticks are of the greatest 

 importance. As external parasites, the constant irritation 

 caused by their attacks, combined with the serious drain 

 on the host's system, occasioned by considerable loss of 

 blood, leads to an emaciated condition and general want 

 of tone. 



In order that ticks may reach maturity and increase 

 their kind, it is essential for them to suck blood, and, 

 to do this, they must become attached to some animal; 

 unless they are able to find a host within a reasonable 

 period, they starve. This fact has been utilised in America, 

 by establishing a rotation system of farming, in order 

 to starve out Margaropus annulatus, a tick responsible 

 for Texas fever in cattle. In brief, the life-history of 

 every tick consists of egg, larva, nymph, and adult, and, 

 in nearly every case, engorgement must take place just 

 prior to oviposition, though the spinous ear tick, Ornitho- 

 dorus megnini, drops from its host as an engorged nymph, 

 moults to the adult form, and deposits eggs without any 

 further engorgement. In the genus Argas, or shining ticks, 

 the nymph engorges twice before moulting. Behaviour at 

 or after oviposition also varies considerably ; in some species 

 the females die immediately after depositing their quota 



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