The majority of blackflies (family Simuliidae) are blood- suckers of man and domestic animals. Throughout the vast territory of the Soviet Union, in the steppes, forest steppes, and especially the taiga and tundra, blackflies occupy a prominent place among the blood-sucking Diptera. It is now clear, that not only in the tropics but throughout the Soviet Union, blackflies are transmitters of several diseases of domestic animals, mainly onchocerciasis of cattle and reindeer and many dangerous diseases of domestic fowl. Hence blackflies are of medico-veterinary and sanitary-epidemiological importance. Unlike other blood-sucking insects such as the malarial mosquito, blackflies have hitherto been relatively poorly studies. The purposes of the present volume is to provide a brief description of species and new identification keys. It primarily incorporates numerous additions to the first edition of "Fauna of the USSR," This second edition also includes 18 species from countries adjoining the Palearctic region, which have not been recorded to-date in the Soviet Union, and 30 species described by Enderlein from Europe (whose description has been improved upon) which may be discovered later in the Soviet Union. The fauna of the USSR currently includes about 300 species of blackflies.