What are the witches' strenghts?

The witches were dark powers meant to cause disorder and chaos. Their strengths lay in their powers of manipulation over the weak minded like Macbeth. They spoke in riddles and equivocation meant to, as Banquo put it, "Win us with honest trifles, to betray's. In deepest consequence ". Witches had the power for spells and tricks. They seem to have slight control over the elements (weather) but not able to directly take lives.