Aragog the Acromantula is released into the Forbidden Forest

Hagrid has been raising the baby Acromantula in a cupboard in the Hogwarts dungeons, but his arrangement is revealed to the teachers by Tom Riddle, suggesting to them that the Acromantula was responsible for the death of Myrtle Warren. Hagrid is expelled from Hogwarts for supposedly causing the death of a student.

Hagrid will later find Aragog a wife, Mosag, and together the two Acromantulas will establish a colony in the Forbidden Forest (CS15).