Creeper

Creepers were giant mobile plants cultivated and controlled by the Kleptons. Their thick, strong bodies were able to smash whole buildings and could move quickly.

In the 30th century, the Kleptons attacked a Thain city, using their creepers to destroy many of their buildings. After a second attack was repelled with the aid of the First Doctor, John and Gillian, one of the creepers grabbed John, but the Doctor killed it with a heat gun. When the time travellers began following the Kleptons to their underwater city, another creeper tried to stop them by pulling a building down on top of them, but they evaded it with only inches to spare. In the Klepton city, the Doctor found creepers in a giant machine, which were freed when Klepton guards firing on him accidentally struck the machine. The Doctor first directed the creepers to attack the Kleptons, then to destroy the city's reactor, which exploded, destroying the city and killing all the Kleptons. (COMIC: The Klepton Parasites)