MITES 229 



Ticks (Ixodoidea) 



Ticks are really only large mites which may reach a length of half 

 an inch or more when gorged. There ^re about 300 different species in 

 the world and as a group they are not really successful. Sometimes, 

 however, a single species is present in fairly large numbers. It was 

 estimated that in certain parts of the U.S.A. there were 2,800,000 

 feeding ticks to the square mile, parasitizing the snow-shoe hare and 

 ruffed grouse, but this is nothing compared with certain mites which 

 may number several thousand to the square inch. 



A few species are confined exclusively to birds, although a fairly 

 high proportion feed on both mammals and birds and in their larval 

 stages some regularly attack ground-nesters, such as larks and plovers. 



There are two groups of ticks which have adopted rather different 

 types of lives. Members of the family Argasidae, which are tough and 

 leathery with gorgeously embossed integuments, live and breed in 

 nests and burrows, and feed at night when the bird or mammal returns 

 to rest. They engorge very rapidly and therefore do not have to leave 

 the habitation of the host. They are found mostly in warm and tropical 

 countries and in the rigours of the British climate they seek out a species 

 like the domestic pigeon, which lives in sheltered dove-cotes. Members 

 of the other family of ticks, the Ixodidae, which have a dorsal plate or 

 scutum on their backs, are not nest dwellers and depend for food on a 

 chance meeting with the host as it wanders about in the fields and woods. 

 They engorge slowly and therefore spend a considerable amount of 

 time actually attached to the bird's body. The fully fed female of the 

 most famihar British species, the sheep tick, /. ricinus (Plate XXXII) 

 looks like a shiny blue pea sticking firmly to the skin of the host. The 

 mouth-parts are deeply embedded in the flesh and on account of the 

 recurved spines (Plate Xlld) which anchor the rostrum in position it is 

 extremely difficult to dislodge. This a typical adaptation to the para- 

 sitic mode of hfe and impressed the early naturalists. Thomas MoufTet 

 wrote, '' For Tykes will sometimes enter deep into the skin with their 

 nose, that you can hardly pull them out but with the loss of their heads 

 and they seldom wander but they bite cruelly and make themselves a 

 hollow place and there they stand fast." In addition to the spined 

 rostrum (Plate XI Id), ticks have suckers between their claws which 

 assist them in clinging to the host, especially before they become 

 fixed and in their larval stages. 



