The Bookworms

From Muppet Wiki

The Bookworms were three female worms who performed as singers on Sesame Street. Unlike Slimey, they were actually hand puppets. They performed in front of a book-like background, which helped to create the illusion that they were small.

They sang "I'm a Bookworm, Baby!" in a sketch in 1991 with the lead singer, an orange worm, voiced by Ivy Austin.