CHAPTER XXVI 

 THE WATER-MITES (HYDRACARINA) 



By ROBERT H. WOLCOTT 



Professor of Zoology in the University of Nebraska 



Conspicuous among aquatic organisms on account of their 

 activity and the brilHance of their coloring are the water-mites, 

 forming the group Hydracarina. These attractive httle creatures 

 may be met with in water almost anywhere, but being carnivorous 

 and thus dependent on the presence of much animal life, and hav- 

 ing a life-time extending over a number of months, they are found 

 regularly and in abundance only in pools which are moderate in 

 depth, permanent in character, and which possess a considerable 

 plant growth. There in the vegetation of the bottom and the shore 

 they live, clambering about over the surface of the plants, swim- 

 ming across from one stem or leaf to another, and feeding on 

 Crustacea, insect larvae or other animals which they may be able 

 to overpower and capture. A few species are pelagic, spending 

 most of their time in the open water of the lake or pond, while 

 other forms, as Tyrrellia, are found wandering over the moss and 

 debris which accumulates along a swampy portion of the shore. 

 Feltria is a genus containing small forms that are found only in the 

 mountain streams of Europe; yet in general water-mites are not 

 abundant in flowing streams except in sheltered places where there 

 is a growth of vegetation which protects them from the rapid cur- 

 rent. Two genera are parasitic in fresh-water mussels, and the 

 larvae and pupae of others attach themselves to aquatic insects or 

 other animals. Most of them are fresh-water forms, but a very 

 few have been described which are marine and a few others have 

 accustomed themselves in certain localities to life in brackish water. 



Hydrachnids are generally distributed over the world but seem 

 to reach the greatest abundance in the clear, cool waters of the 

 spring-fed lakes and pools, rich in plant hfe, which are so charac- 

 teristic of all temperate latitudes, and which dot our northern states 



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