In that vein: inflated wing veins contribute to butterfly hearing.

Insects have evolved a diversity of hearing organs specialized to detect sounds critical for survival. We report on a unique structure on butterfly wings that enhances hearing. The Satyrini are a diverse group of butterflies occurring throughout the world. One of their distinguishing features is a conspicuous swelling of their forewing vein, but the functional significance of this structure is unknown. Here, we show that wing vein inflations function in hearing. Using the common wood nymph, Cercyonis pegala, as a model, we show that (i) these butterflies have ears on their forewings that are most sensitive to low frequency sounds (less than 5 kHz); (ii) inflated wing veins are directly connected to the ears; and (iii) when vein inflations are ablated, sensitivity to low frequency sounds is impaired. We propose that inflated veins contribute to low frequency hearing by impedance matching.