Heliconius butterflies have undergone adaptive radiation and therefore serve as an excellent system for exploring the continuum of speciation and adaptive evolution. However, there is a long-lasting paradox between their convergent mimetic wing patterns and rapid divergence in speciation. Here, we characterize a locus that consistently displays high divergence among Heliconius butterflies and acts as an introgression hotspot. We further show that this locus contains multiple genes related to locomotion and conserved in Lepidoptera. In light of these findings, we consider that locomotion traits may be under selection, and if these are heritable traits that are selected for, then they might act as species barriers.