This backwardly-mobile dung beetle uses its back legs to move the "dung", which is a brown ball of yarn.
This model is from the book, "NXT One-Kit Creatures", by Fay Rhodes. The book includes full-color building and programming instructions for five animals, which can be built using either the NXT 1.0 kit OR the NXT 2.0 kit. In addition to the dung beetle, the book includes building instructions for an undulating shark, a crawling horseshoe crab, a walking chick and a leaping grasshopper. More information is available on Fay's web site.