rivers in valleys. Hydropsyche ornatula emerged in large numbers 

 in the Volga before its reconstruction, and at present they emerge in those 

 parts of the Volga which have retained their river character; this is true 

 also at the Oka and other tributaries of the Volga which have retained their 

 natural character. Large numbers of Arctopsyche ladogensis and 

 Hydropsyche nevae hatch in early summer in the Neva and Svir' 

 rivers. Great numbers of Macronematinae (M a c r on e m a radiatum, 

 Aethaloptera rossica) fly along long stretches of the Ob, Yenisei, 

 and Amur. Caddis flies emerge in enormous masses in Lake Baikal. 



ENVIRONMENT 



Ecological differentiation of caddis flies 



The Trichoptera are an ancient order which were already differentiated 

 in the Permian (Martynov, 1938); during their long existence, they passed a 

 complicated evolution, connected with the formation of continents and changes 

 in the hydrographic network of the land. While adapting to changing 

 habitats, the larvae settled in a wide range of water bodies. They became 

 adapted to the different biotopes of running water or stagnant water, and 

 developed various morphological and physiological adaptations; they also 

 104 developed a high ecological differentiation. In addition to narrowly 



specialized species restricted to a few biotopes, large groups of ecologically 

 flexible species have a wide ecological range and live in variable conditions. 



Below, we describe the relation of Trichoptera to different factors 

 of the aquatic environment. The habitats of Trichoptera in different water 

 bodies and biotopes are described in the next chapter. 



Degree of mineralization of water and 

 organic matter 



Adaptation to different degrees of mineralization of water affects the 

 physiology of the organism markedly; it requires changes in the osmotic 

 pressure of the body fluid, modification of the osmoregulatory process and 

 reconstruction of the organs concerned. Caddis flies live mainly in 

 continental fresh water bodies of the calcium hydrocarbonate group with a 

 prevalence of HCO3 anions and the Ca 2+ cations and with a small content 

 of chlorides. The range of water bodies inhabited by caddis flies is very 

 wide and includes snow streams in mountains, sphagnum lakes, some 

 mountain lakes with low mineralization, as well as the hard, highly 

 mineralized water of some lakes (e. g., Sevan Lake with a mineralization of 

 662 mg/l), and water bodies with an underground feed. Caddis flies widely 

 inhabit fresh (ahaline) and oligohaline water bodies; they also occur in 

 mesohaline waters, and are found, for example, near the coast of the open 

 western part of the Gulf of Finland, with a salinity of 5— 6%o (Siltala, 1906:9) 

 where several forms of the ordinary lake fauna occur (they are widely 

 distributed on the fresh-water littoral of the Gulf of Finland), and also 



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