Black Widow House
Informally nicknamed the Darners, on the grounds that they'll all end up as Seamstresses some day.
The Black Widow is one of the deadliest poisonous spiders to be found on Roundworld. It must evidently have a Discworld analogue, as its use in this context does not seem to be accidental. Like all spiders, the Black Widow is larger and deadlier than the male, and once the male has ceased to be of use while alive, the female will not think twice before killing and devouring him. In fact, she may not even think once.
In general, in the British public school system of which the Discworld schools are a reflection, a house name is conferred as a sort of exemplar, which house members are expected to ponder the meaning and significance of and model themselves upon. It can be a person or quality or animal seen to have perceived virtues and graces which the pupils are expected to assimilate. Therefore Black Widow alumni should be more than usually avoided?