The vilkacis is a werewolf in Latvian and Lithuanian mythology.
Vilkacis litterally means "wolf's eyes" 'werewolf'. Alternative names include Vilkatas, Vilkatis.
The vilkacis is a human that shapeshifts into a werewolf, however it is not clear wether there is a physical transformation or the soul enter the body of a wolf. Some tales mention an apparently asleep person who appeared at miles "running like werewolf", after what the person turns out to be dead, as the soul couldn't enter the flesh to return.
Although mostly malevolent, on occasion the vilkacis would bring treasures or be beneficial.
In the Latvian mythology, particulary women would be the ones, who turn into Vilkacis. They have to strip completely and then leave their clothes in a place, where noone would find them, for, if someone touches them, Vilkacis can't turn back into human for some time ( particulary the time is considered to be 1 to 9 years ), and in this case they would run around the house, specially, if they had a child, and houl and sometimes come closer to their husbands and children.
They say, that you can turn into Vilkacis yourself without someone of them biting you - all you have to do is wait for full moon, and go under a tree, thats' top has been grown into earth, forming an arch. Then you transform into Vilkacis, although is not clear, how you get back to your original human form after that...