CHAPTER VII 

 GALLS CAUSED BY MITES (ACARI) 



MITES and ticks are included in the order Acari. The 

 systematic position of this order is in the class 

 Arachnida, which also includes scorpions, spiders, and 

 harvest spiders. Mites and ticks are creatures of such 

 peculiar organization that they seem far removed from the 

 other members of the Arachnida, but they appear to bear 

 some affinities with the harvest spiders. 



The order contains two groups, the typical mites and 

 ticks {Acarina) and the worm-like group (Vermiformia). Gall- 

 causers occur only in the latter group. In the Acarina the 

 larva has at first only three pairs of legs, it acquires 

 later the fourth pair; eyes are usually present. In the 

 Vermiformia there are no eyes and no tracheae. In some 

 species the adult has four pairs Of three-jointed legs, 

 but in the family which contains the gall-mites the 

 third and fourth pair of legs are missing; the first and 

 second are placed on the forepart of the body, which is 

 long and furnished with bristles arranged more or less 

 symmetrically. 



The Vermiform mites are very minute, and are often over- 

 looked in the absence of microscopic examination for them. 

 The species known as Eriophyes fraxini, which is responsible 

 for the curious fasciations of the flowers of the Common Ash, 

 is one of the pigmies of this pigmy race ; it is quite invisible 

 to the unaided eye, and may be best seen by washing a gall 

 in a little water and examining a drop of the fluid under a 

 J-inch objective. 



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