Familars

Latin: famulus
A familiar, or an imp, is an attendant subordinate demon in the form of an animal. Such creatures drew nourishment by suckling from devil’s marks, a witch's breasts, or insensitive parts on a witch.
Familiars behaved in ways that no natural pet was believed to. They ran errands, brought messages, and aided in devil worship.
The following are some of the creatures believed to have been used by witches as familiars: cats, dogs, toads, wolves, bees, bats, blackbirds, owls, spiders, flies, chickens.