Ultrasonic clicks produced by the peacock butterfly: a possible bat-repellent mechanism

Torpid peacock butterflies (Inachis io) produce intense ultrasonic clicks that startle captive vespertilionid bats (Plecotus auritus and Pipistrellus pipistrellus). The clicks occur as the wings are opened and are generated by a stiff portion of wing membrane between the costal and subcostal veins near the base of the forewing. The power spectrum of a click matches the most sensitive area of a bat's audiogram. Clicks may serve as acoustic equivalents of the attack-retarding eyespot display in the same species.