The Earthworm Jim theme tune was written, orchestrated and conducted by William Anderson - he even sung the lyrics himself in the TV show introduction. There is more information on his IMDB profile about the other work he has done in the animation, film, theatre and video games. See the Links for relevant external sites.
Through soil he did crawl,
A supersuit did fall!
Jim was just a dirt-eating, chewy link of worm flesh,
but all that came to a crashing end, ha ha ha! Ahhh!
He's such a groovy guy,
He rockets through the sky!
Cruisin' through the universe, having lots of fun,
here comes Earthworm Jim you know that he's the mighty one!
~ Brief whistling interlude where Jim swallows a butterfly ~
Despite his great big muscles and his really big ray-gun,
Jim is just an earthworm but then he's the only one
with a supersuit to make him really super-strong!
Jim can be a winner if we only sing along!
We think he's mighty fine!
A hero for all time!
Earthworm, Earthworm, Earthworm, Earthworm Jim!
Hooray for hiiiiiiiim!!