118 ACAKINA OR MITES. 



is referred to Murray's excellent ' Economic Entomology,' which 

 deals with spiders, mites, amd other Arachnoidea. 



Ararina or Miten. 



The mites are of great importance, as many of them are para- 

 sitic, not only upon animals and man, but upon plants. The 

 Acarina are mainly very minute animals, many being no more 

 than aiflth of an inch in length ; and yet it is these minute 

 forms that cause the most serious pathologic disturbances in 

 animals (Scab, Mange, Itch, &c.) and the most serious plant 

 diseases (Big Bud, Eed Spider, &c.). In all mites, and the 

 similarly grouped ticks, the head, thorax, and abdomen are 

 united more or less into one solid body. The internal parasitic 

 forms are generally white or pale-creamy colour. They are pro- 

 vided with a biting and piercing mouth. Amongst the more 

 important diseases produced by them are sheep-scab, mange, and 

 itch. They also affect poultry, causing feather-eating, scaly-leg, 

 and in plants various " galled " appearances only too common 

 on some of our fruit-trees. Some are predacious, and so bene- 

 ficial. There are also species that live in the water. These 

 latter we need not refer to again. Most mites, like spiders, 

 have four pairs of legs when mature, the young having only 

 three pairs. The more or less fused head, thorax, and abdomen 

 soon separate them from the spiders. The so-called red-spider of 

 the hop, TetranijcTius malvi', and the red-spiders of fruit, the 

 Bryohia ribis, &c., can thus be readily seen to be acari and not 

 araneida. Nearly all acari produce ova : some few are, however, 

 parthenogenetic, and produce living young. The following are 

 the groups of some importance to the farmer, fruit grower, and 

 gardener : — 



(i) Tromhidiihr, the so-called Spinning INtites or Eed-spiders. 

 These are found on the leaves of plants, and constitute the 

 group Tetranychi (fig. 51), which can be told by their small 

 size and usually semi-transparent bodies, sometimes however 



