Acromantula

Huge, poisonous spiders covered in a thick black hair might not be every wizard’s idea of an ideal pet, but this did not put Rubeus Hagrid off the idea. As a Hogwarts pupil, Hagrid cared for a young Acromantula named Aragog, but was ultimately forced to release him into the Forbidden Forest where a large colony was established. With a leg span reaching up to fifteen foot, capable of speech and willing to eat humans who stray into their territory, the spiders are believed to have been initially bred by wizards, intended as guards. As Hagrid discovered, it was possible to befriend them though.