According to a belief among the Carpathian Ukrainians, the devil can turn into a fly (present-day Ivano-Frankivsk Oblast, Pechenizhyn). The Poles have legends about a “3MOpe” fly that suffocates sleeping people at night (Skierniewice Voivodeship, Bartniki, ArchKEUW O/7: 2). Among the Czechs, “Mapa” can turn into a large black fly. A witch can also take the form of a fly to steal milk from other people’s cows (Velyashkovichi, Nikif.PPP: 249). To recognize a witch in fly form, one must watch for her restless movements and catch her—tie her up in a dedilka and hang her above the stove opening or air vent; the witch will die in agony (ibid.: 274).

The belief in the soul as a fly is widespread among the Slavs. The image of the witch as a fly is connected with the fly form taken by her soul. Among Russians and South Slavs, stories about a soul flying out of a witch in the form of a fly are popular (Haase VBO: 381, Voronezh Governorate, Af.PVSP 3: 218). Similar stories have been recorded on the island of Krk and in the Kastav region, Dalmatia, Poljica, and Sinj (Milé. VOBMP: 236, Ivan.P 10: 228, Vul.-Vuk.P: 163–164, ibid.: 158–159).

— Gura. Animal Symbolism in the Slavic Folk Tradition, p. 438