Insect

Insects were a class of animal. Insects or analogues to them, some sentient, appeared on Earth and many other planets.

The Wirrn were sapient insects native to the Andromeda Galaxy. (TV: The Ark in Space)

On Earth, the population of insects was many times greater than humanity. It was mentioned that had Miracle Day, which caused death in humans to cease to exist, affected insects, they would have overrun the Earth in 48 hours. (TV: The New World)

On one planet, a crashed spacecraft spilled fuel which caused nearby insects and other life forms to mutate to giant sizes. These mutants plagued the native Meerags until the Fourth Doctor arrived and helped destroy them with fire. (COMIC: The Mutants)

The First Doctor did not like insects, and was thus frightened of the Menoptera when he first encountered them. (PROSE: The Lost Ones)

Insecticide was used to kill insects. (TV: Planet of Giants)