In the forest-steppe zones, the bloodsucking dipterans--midges (Diptera, Simuliidae)--tend to drastically increase in size, which poses medical and veterinary problems (the toxic saliva administered into the victim's body on blood sucking causes diseases in man, disability, and even animals' death). According to our data, the role of dominating bloodsuckers varies in different districts of the Voronezh Region, depending on their Iocal conditions (the types of water systems and landscapes).