From Huai-Ti Lin, Gary G. Leisk, and Barry Trimmer of the Departments of Biology and Mechanical Engineering at Tufts University:

[S]ome caterpillars can curl into a wheel and generate their own rolling momentum as part of an escape repertoire. This change in body conformation occurs well within 100 ms and generates a linear velocity over 0.2 m s?1, making it one of the fastest self-propelled wheeling behaviors in nature.

Their paper is available for free from IOPscience for 30 days, with registration. ScienceNOW has video of the model organism, and the model behavior, that inspired this impressive means of locomotion. [Thanks, Alan Dove!]