CHAPTER IX 



THE ORDER ACARINA: MITES 



THE term mite is conveniently, though somewhat loosely, applied to a 

 large assemblage of acari, mostly of small, often minute, size, contained 

 in the order Acarina, the family Ixodidae being excluded. Mites are 

 widely distributed in nature and are both terrestial and aquatic in habit ; 

 the species are most numerous in temperate zones and may be found 

 at great altitudes. The majority are free-living ; a few, however, are 

 parasitic and are found on a great variety of hosts, including mammals, 

 birds and insects ; some species are parasitic in their immature stages and 

 free-living in their adult stages, and a few utilize insects as a mode of 

 transport from one breeding ground to another. With the exception 

 of the Ixodidae, the acari have attracted very little attention from 

 naturalists, and detailed information, especially with regard to their 

 biology, is very scanty. 



Many of the Gamasidae are true blood-suckers, and have habits similar 

 to those of the ticks, to which they are closely related. They may there- 

 fore act as the transmitters of blood parasites, and one 



. , . . . .... Relation to disease 



instance of this is known, that of the transmission ot 



Leucocytogregariiia inuris by Laelaps echidninus. Among the Trom- 

 bidiidae there are several imperfectly differentiated species which cause 

 skin eruptions at certain seasons in those exposed to their bites. The 

 family Sarcoptidae includes the mites which cause scabies in man and 

 corresponding diseases of the skin of animals, while Demodex folliculorum, 

 a vermiform acarian, which lives in the sebaceous glands and hair fol- 

 licles of man, is believed by Borrel, though on somewhat slender evidence, 

 to be associated with the spread of cancer and leprosy. A species of 

 Trombidium, T. akamushi, Brumpt, is said to be associated with the 

 disease known as Japanese River Fever or ' Tsutsugamushi ' disease. 

 People who handle cereals are sometimes affected by an eruption due 

 to a species of Pediculoides which lives in the grain. 



FAMILY GAMASIDAE 



Body flat and broad, and furnished with plates and shields as follows: 

 A pair of plates, the jugitlaria, just behind coxa I on the ventral surface ; 



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