Big Green Caterpillar

Worms are thin, tube-shaped creatures. Fictitious versions of them have been adapted for the Mario series based off of the non-fictional creatures.

The Super Mario Bros. Super Show!
A single worm first appeared in the The Super Mario Bros. Super Show! episode "The Bird! The Bird!". After the Mario bros. defeated Bowser and saved their new friend Cheepy and his mother, they were invited over to Cheepy's house for dinner as thanks for their help, however they were unaware that the dinner was actually a large talking grumpy worm, after seeing it they ran out of the house.

Super Mario Bros. film
In the Super Mario Bros. film, worms were used as sustenance and drink toppings for the people of Dinohatten. Lena, one of the main antagonists of the film was seen drinking a worm as it screamed for mercy, showing that the worms of Dinohatten are indeed intelligent.

Wario Land 3
In Wario Land 3, a worm named Wormwould appeared as the boss of The Grasslands and Wario had to defeat him in order to gain the Music Box that opened the way to The Big Bridge.

Super Mario Galaxy
In Super Mario Galaxy, a giant friendly green worm appeared in the Gusty Garden Galaxy where it was snaking on some apples. Mario could use this worm to cross between the many apple planets in the area.