Black Widows are known foremost for their ability to see visions. They do this by constructing Tangled Webs , through which they see both symbolic and actual images of the future which they must then interpret. They are also proficient with poisons and illusions. In addition, they have a poisonous snake tooth under the nail of the ring finger on their right hand. The power of the venom is in proportion to the power of the witch, and it has to be milked regularly, or the venom will crystallize and cause pain.
The hourglass was the Black Widows' symbol, both a declaration and a warning about the witch who wore it. An apprentice wore a pendant with the gold dust sealed in the top half of the glass. A journey maid’s pendant had the gold dust evenly divided between top and bottom. A fully trained Black Widow wore an hourglass with all the gold dust in the bottom chamber.
Black Widows are normally a "natural" phenomenon. However, it was made clear by Saetan SaDiablo that a Black Widow could be made when he learned the Hourglass Craft from Cassandra. Jaenelle, Daemon, Karla, and Gabrielle are all stated as 'natural' black Widows who were born with the gift.
Black Widows were heavily persecuted in Tereille under the influence of Hekatah before the Purge, although she herself was one.