Nebrie are large amphibious creatures that inhabit the swampy regions of Thra. Jen encounters the grub-like creatures when, after being startled by Fizzgig, he falls into a bog. Kira is able to call below the muck to a mother Nebrie, who lifts him out. After it saved Jen, it started to eat on some fern-like plants, so it is most likely that they are herbivores.
However the podlings utilize Nebrie as well. The Podlings domesticate Nebrie for collecting milk, and when a nebrie died the Podlings would waste nothing - its skin would be used to make drums and the patches of fur around its face and ears would be fashioned into clothes for the little podlings.