It has been proposed that a moving hybrid zone can be a mechanism for the spread of adaptive traits in phase III of Wright's shifting balance model of evolution. Here I present an example of a moving hybrid zone in warningly colored Heliconius butterflies, a system which is considered to be a possible case of shifting balance evolution. Having moved approximately 47 km in 17 years, the hybrid zone shift has led to the H. erato hydara color pattern rapidly displacing the adjacent H. erato petiverana pattern. The movement is potentially due to dominance drive augmenting a slight selective advantage of H. erato hydara over H. erato petiverana, which is largely consistent with theoretical conditions favoring the success of phase III.