This article considers the natural regulators of blood-sucking Simuliidae subzone mixed forests on territory Belarus and Ukraine. In forests, major preimaginal phases bloodsucking blackflies are microsporidia (Polidyspirenia simulii, Polidyspirenia sp., Thelohania fibrata, Amblyospora bracteata, A. varians), fungi mermithides (Gastromermis boophthorae). Caddisfly larvae (Hydropsyche angustipenn...