noisy butterflies

September 8, 2005

in Insects,Natural history,Travel

Pan_lep_crack This is a Variable Cracker, Hamadryas feronia, a member of a mostly Neotropical genus of about 20 species.  Variable Crackers are found from the southern U.S. through Brazil, and are one of several species of Hamadryas that can make an audible sound.  Males perch head-down on tree trunks and fly out at passing conspecifics, producing a burst of intense, double-component clicks.  Presumably, this is used for communicating between individuals, and the function may vary between species or even populations. The sounds are not percussive, as was previously thought, since the butterflies are able to make the sound with only one wing.  The mechanism appears to be the buckling of a stiff portion of the wings.

This leads us to the question: can butterflies hear?  It would seem that at least some can.  Many species of the large family of brush-footed butterflies, Nymphalidae, have a structure at the base of the forewing known as a Vogel’s organ, a thin membrane associated with an air sac and a sensory organ, similar to the tympanal “ears” of other insects. This allows them to detect sounds (or vibrations) of various frequencies.  Many species of butterflies have Vogel’s organs (some not well developed) but are not known to produce noise themselves.  There is speculation that Vogel’s organs may have originally evolved as bat or predator detectors, and that some families, such as Hamadryas, are regaining or co-opting the ability to hear and produce sound as a means of communication.

Like many other insects in the tropics, crackers also rely on excellent camouflage — you can see how well they blend in with the bark of trees. Crackers are perhaps one of the only butterflies in the world that might be easier to hear than they are to see!

Yack, J.E., L.D. Otero, J.W. Dawson, A. Surlykke, and J.H. Fullard.  2000. Sound production and hearing in the blue cracker butterfly, Hamadryas feronia (Lepidoptera, Nymphalidae) from Venezuela. Jrl. of Experimental Biology 203: 3869-3702.

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