black widow
n.
1. Any of several venomous spiders of the genus Latrodectus, the females of which have a black shiny body with red markings, often in the shape of an hourglass on the abdomen, and can inflict a dangerous bite.
2. A woman who kills her husband or lover, especially one who kills multiple husbands or lovers.
[From the fact that the female sometimes eats its mate.]
black widowfemale spider