A zebra longwing butterfly (Heliconius charithonia) perched on a branch shows its antennae, legs, and mouthparts, which are organs involved in carrying out chemosensory functions. Ningning Wu et al. investigated the evolution of chemosensing during the stage of speciation with incomplete reproductive isolation in the hybridizing Heliconius species. The results provide a unique perspective and relevant view of the genetic architecture of chemosensing, leading to a better understanding of the magnitude and complexity of molecular changes in sensory tissues that contribute to the establishment of reproductive isolation and speciation. Image credit: Luca Livraghi.