Spider

Spiders were a type of arachnid commonly found on Earth. They were noted for spinning webs which they used to catch prey.

Originally, spiders were small, inoffensive creatures, none growing much larger than a rat. By the 26th century, though, radiation had caused mutations, allowing them to reach much larger sizes. (BNA: Ship of Fools) An example of this were the Eight Legs, spiders with great mental powers, who evolved on Metebelis III from spiders that survived the crash landing of a human ship. (DW: Planet of the Spiders)

K9 once encountered spiders on an unnamed planet in another dimension, partially inhabited by ex-Tellac miners. They lived alongside other Earth animals from widely varying periods of evolutionary history. Unlike most species of spider on 21st century Earth, however, these were as big as gorillas, and their webs spanned between trees. (AK9: K9 and the Missing Planet)

One unnamed planet was home to giant spiders which were controlled by the Master of Spiders. When he used them to attack the Second Doctor, John and Gillian, the Doctor used his ray gun to kill one spider (while shouting "Die, hideous creature... die!") and used his recorder to keep other spiders from attacking them. When the Master was defeated, the Doctor sealed the surviving spiders back in their cave. (TVC: Master of Spiders)