198 



INTRODUCTION TO ZOOLOGY 



CHAP. 



pairs of legs (except in the Gall-mites), but acquires four 



pairs at the last moult before becoming adult. 



Some of the Acarina have a much elongated striated 



abdomen ; these are the Gall-mites which produce little finger- 

 like or pimple-like processes on the 

 leaves of some trees, e.g. the " Nail 

 Galls " on the lime, due to the mite 

 Eriophyes ( = Phytoptus) tiliae (Fig. 

 132); also the small "Ked Pimple" 

 galls on sycamore and maple, due 

 to Eriophyes macr&rhynchus, and 

 similar pimple galls on the leaves of 

 the sallow willow and the alder. 

 Again, the swollen arrested buds and 

 distorted catkins sometimes found 

 on hazel are due to the presence of 

 species of the same genus of mite 

 (Fig. 133). 



The Gall-mites are unlike other 

 mites in having only two pairs of 

 legs, which are placed very close to 

 the head ; the mouth-parts are cap- 



FIG. 133. A hazel twig with a bi e O f biting. The galls formed are 



one single chamber, which is open 

 below, the opening being guarded by hairs. In this cavity 

 many mites live together, feeding on the hairs produced 

 from the inner lining of the gall-cavity. 



Other mites, with short bodies, live on various animal and 

 vegetable matter, e.g. the soft Cheese Mite on cheese ; the 

 " Beetle " Mite (so called from its hard skin) on dead wood or 

 other decaying vegetable matter ; " Ticks " on the blood of 

 various mammals and birds, the skin of the infected animal 

 being pierced by their jaws. Another mite causes the disease 

 called " mange " in dogs. 



The Water Mites are larger, and are fairly common objects 

 in a pond. Specially noticeable is the little scarlet water 

 mite, less than J inch long, which swims so actively ; the 

 larva of this form sucks the blood of water insects and spiders, 

 but the adult feeds on minute crustaceans. 



