Butterflies comprise 3 of 46 superfamilies (Hedyloidea, Papilionoidea, and Hesperoidea) in the order Lepidoptera. Most butterflies are diurnally active, and much research has focused on how they use vision and chemical senses for communication and orientation.
What about a sense of hearing? Do butterflies have ears? Although hearing is well studied in moths, who use their ears to detect the ultrasonic calls of bats, hearing in butterflies is poorly understood.
We are discovering that many butterflies have well developed ears on their wings. Our current research focuses on the evolution, structure, function, and physiology of hearing in this interesting group of insects.
Hearing in Diurnal Butterflies
Many Nymphalidae butterflies have ears and we have confirmed hearing in several species using neuroanatomical and neurophysiological methods. Ears are mostly sensitive to sound frequencies between 500 Hz and 6 kHz, overlapping the hearing range of humans. The function of hearing in diurnal butterflies is not understood, and we are testing two hypotheses : conspecific communication and predator detection.
The 'blue cracker' butterfly, Hamadryas feronia is believed to communicate acoustically with conspecifics, since this species produces loud clacking sounds during conspecific interactions (see Yack et al., 2000- pdf download).
Most species however, do not generate sounds, and we hypothesize that they are listening to the flight sounds, or possibly the foraging calls of predatory birds. The well known Morpho species for example possess ears (see Lane et al. pdf download; Lucas et al. pdf download) that respond to the sounds made by birds during flight (Yack lab, unpublished).
Hearing organ in Morpho butterflies (left). Circle on middle photograph indicates location of the ear. Image to the right is a scanning electron micrograph of the ear.
A & B. Hearing organ in Morpho butterfly showing laser scanning points. C. Vibrations of the membrane responding to 2.5 kHz. D. Sensory organs innervating the ear. E. Neurophysiological responses of the auditory nerve to 2 and 6 kHz sounds.)
Hearing in Nocturnal Butterflies
The hedylids are nocturnally active butterflies that live in the neotropics, and are special because they are believed to represent the ‘living ancestors’ of diurnal butterflies. We have described an ultrasound-sensitive ear on the ventral surface of the forewings (Yack & Fullard, Nature, 2000, pdf download; Yack et al. JCP 2007, pdf download). We are currently studying the neuroanatomy, physiology, and taxonomic distribution of these interesting ‘wing ears’.
Our studies on the Hedyloidea have been carried out at the Smithsonian Tropical Research Institute in Panama.
Ears in nocturnal butterflies (Hedyloidea). Left, arrow points to location of the ear. Middle, scanning electron micrograph of the tympanal membrane. Right, scanning micrograph of three chordotonal sensory organs attached to the inner surface of the tympanal membrane