Bat

Bats were nocturnal, flying mammals found on Earth. They were feared by some humans, who believed that they drank blood. However few species of bats actually did so.

Many vampire legends told of vampires turning themselves into bats and back into their true forms.

Encounters with bats
Whilst on the run from the Daleks, the First Doctor, Ian, Barbara and Vicki landed in a faux-haunted house. Built for the Festival of Ghana, the building housed replicas of classic fictional monsters like Dracula. The house was also infested with bats, groups of whom occasionally took flight so as to add to the general spooky environment of the "haunted house". (DW: "Journey into Terror")

During the time he travelled with John and Gillian, the First Doctor again encountered bats. Soon after landing on the Haunted Planet, bats attacked John. The Doctor successfully shooed them away with a big stick, but he surmised that the bats were being controlled by someone evil. (TVC: The Haunted Planet)

The First Doctor, John and Gillian briefly encountered a bat in a cave on a desolate planet. (TVC: Shark Bait)

Florence Stoker had the ability to control bats and used them to block the sunlight, allowing her to go outside during the day. (DWA: Bat Attack!) At one point, bats lived in the Cloister Room of the Doctor's TARDIS. (DW: Doctor Who) Their names were Jasper and Stewart. (EDA: Vampire Science, Seeing I)

Aukon used bats as servants in his kingdom. He sent them to attack the Fourth Doctor and Romana. The Doctor claimed they were harmless shortly before he was bitten. They travelled in a flock of many thousands. Later, Romana was also bitten by a bat while in a trance. (DW: State of Decay)