Earthworms were a type of invertebrate found on Earth.
The First Doctor once encountered homicidal earthworms which excreted nitrous oxide. Aldridge recalled the incident as "hilarious". (PROSE: A Big Hand for the Doctor)
In 1964, DN6 was tested in Forester's garden, killing an earthworm along with all the other animal life. The First Doctor and Barbara Wright later discovered the dead worm. (TV: Planet of Giants)
Brock offered the Sixth Doctor and Frobisher a worm. The Doctor declined the offer but Frobisher accepted. (COMIC: Once Upon a Time Lord)