The vjestitza (plural: vjeshtitze and sometimes spelled as vestizsa) is a female witch in the lore of Montenegro and Serbia, whose main prey was infants but were also sometimes blamed for adult illnesses.
The vjestititza is typically an old woman whose soul leaves her body at night when she goes to sleep. Her soul then takes the body of a hen , a black moth, or a fly. In this form, she enters houses and feeds upon the blood in the heart of her victims.
On certain nights, the vjeshtitze in such forms meet together in the branches of trees to hold coven meetings. An old woman may join such a coven if she agrees to follow the rules prescribed by the veteran members. The vjeshtitza were most powerful during the first week of March.
A protective ritual during this time was to stir the ashes in the hearth of the house with two horns which were then stuck into the pile of ashes. Like the witches of Western Europe, it was believed that a vjeshtiza could not drown. So, when a woman was accused of being such, she was sometimes bound and cast into water. If she floated, she was guilty. If she drowned, she was innocent.
Two early twentieth century sources on this are: the article Of Magic, Witches and Vampires in the Balkans in the journal Man (December, 1923) and the book Hero Tales and Legends of the Serbs by Woislav. M. Petrovich (London: G. Harrap & Co. Ltd., 1914, 1915, 1923).