Slimey's earliest known appearance is in a second season episode in which Oscar enters Slimey in a Sesame Street Pet Show. A study done in 1971 by Children's Television Workshop's research department reviewed children's responses to this episode, and specifically noted that the children "were attentive, responsive, and loved Slimy, the worm." Slimey's family includes his baby sister Sloppy, his parents Dusty and Eartha, and cousins Squirmy and Rachel. Sloppy is referred to as Stella in a 1985 episode. In a 2008 episode, Slimey got a pet bug named Dirty.