THE :\IORE IMPORTANT FAMILIES OF ACARl. 



Ill 



•still smaller than themselves, and as these are for the most part injurious to 

 plants, the Parastigmata must be considered as useful organisms. — They 

 are to be found everywhere, especially among low herbs, grass and decaying 

 leaves, but also on the undersides of growing leaves, which often swarm with 

 noxious mites. Their biology and anatomy are almost the same as those of 

 the foregoing group, to which they are closely related, with this exception, 

 that they do not occur on mammals or birds, nor in groceries. When the 

 nymphs (eight-legged immature stage) use Insects as a means of transport 

 (see above, section 4), they attach themselves upon them by means of a 

 pellucid elastic stalk, which is formed by a secretion from two stalk-glands, 

 iiankiiig the anus ; hence the name of Uropodoidea, or Stalked Mites. The 

 legs are short and can generally be fitted into depressions or pits on the 

 ventral side of the body (fig. 7). If the mites are found attached to Insects 

 either the whole insect should be preserved in spirits, or the mites may be 

 carefully scraped off with a small knife and preserved alone. 



(6) Heterostigmata are minute, transparent, rarely rose or orange- 

 coloured, extremely weak creatures, with stinging and sucking mouth-parts. 

 As the males lack stigmata, the name of Heterostigmata is proposed for 

 this group. Those of the females are situated between the first pair of legs 



Fig. ^.—Pelicuhldes spinosus (Kramer) ; female ; dorsal and ventral side ; S = stigma. 

 Original. — Noxious species. 



and the maxilla?. Their eight legs are placed in four groups of two. — They 

 all suck plant-juices ; so they are, if they occur in abundance, which is often 

 the case, exceedingly noxious to cultivated plants, and if they have the 

 opportunity to crawl upon men, they cause a most insupportable itching and 

 redness of the skin (erythema). — The pregnant females become enormously 

 distended. They exhibit an anatomical peculiarity in possessing what are 



