CHAPTER VIII 



THE ORDER ACARINA: IXODIDAE OR TICKS 



THE Acarina or Acarians often loosely spoken of as Acari or Mites 

 compose one of the largest and most important orders of the Phylum 

 Arthropoda. They are closely related to the Spiders and Scorpions, 

 especially to the Solpughids, large spider-like arthropods popularly known 

 in India as ' jerrymungulums '. 



In addition to many Acarians which cause troublesome skin diseases 

 (acariasis) of animals, there are more than 200 species, belonging to the 

 family Ixodidae or ticks, which are entirely blood-sucking in habit; no less 

 than eighteen species of these are known to transmit pathogenic parasites 

 to man and the domesticated animals. The order Acarina also includes a 

 number of blood-sucking mites or acari, which, except for a few parasitic 

 on rodents, have been very little studied. The mites which cause 

 damage to crops and stored provisions are, however, much better known. 

 The ' Harvest Mite', 'Harvest Bug', 'Rouget', or ' Red Flea', the well- 

 known Trombidium holosericeum, is familiar in the harvest season in 

 Europe and England. In the tropics, particularly during the rainy season, 

 the worker may encounter numbers of the large ' Plush ' or ' Velvet mite ', 

 another species of Trombidium. During the course of breeding experi- 

 ments with Diptera, many species of mites parasitic on Musca, Stomoxys, 

 Philaematomyia, Psychoda and mosquitoes are met with. In Madras 

 it is not uncommon to find a specimen of Philaematomyia insignis with 

 a dozen or more mites fixed to various parts of its body. In some cases 

 these arthropods greatly interfere with breeding experiments ; very little 

 is known as to what effect they may have on their hosts. 



For the most part Acarians are of small size. The body is compressed 

 dorso-ventrally, seldom elongated, and shows no distinct head, thorax or 



abdomen ; in a few forms the head and thorax (cephalo- 



., .. j < _i i j i r General structure : 



thorax) is separated from the body by a groove or turrow; The mouth parts 



the body may or may not be covered by a chitinous 

 plate the dorsal shield or scutum. At the anterior end of the cephalo- 

 thorax there is a well-marked depression known as the camerostema, 

 into which the mouth parts are inserted ; the latter are often spoken of 



