Educational Materials & Marketing Services
Extension 4-H Youth Bldg.
Ames, Iowa 50011-3630
(515) 294-9915
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Educational Materials & Marketing Services |
1/30/04
Contacts:
Mary Harris, Reiman Gardens, (515) 294-2567, maharris@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Crackers on the Wing
Mary Harris
Christina Reiman Butterfly Wing Curator
Butterflies are not only beautiful to see, but they also can be fun to hear. That’s right, some butterflies on exhibit at Reiman Gardens produce sounds to which visitors can listen.
These sound producing butterflies in the exhibit are collectively called Crackers. To me the cracks sound like a cross between the sounds of a cicada and static electricity. These cracking sounds are produced primarily produced by the males; however, in some species the females also are noisy.
Crackers are members of the Nymphalid family, which contains the brush-footed butterflies. There are eight species of Crackers, all in the genus Hamadryas. These butterflies occur in South and Central America and southern North America. Several species have been seen on occasion in Texas and Arizona, but are considered rare.
Although Crackers are not as large or flashy as some of the other species in the Butterfly Wing, they display behaviors that make them excellent exhibit animals. Crackers perch on flat, vertical surfaces with their heads oriented downward and their wings completely spread and oppressed to the substrate. Once they settle, they remain motionless. The upper sides of the wings of the majority of Cracker species can be recognized by the intricate checkerboard pattern of blues and greys.
Two species, Hamadryas amphinome (the Red or King Cracker) and H. februa (the Grey Cracker), are easily seen by visitors in the Butterfly Wing. Males perch as described above until another male or a female flies near. Then the perching male will take flight and engage the passing individual in some aerial acrobatics while making its signature cracking sounds.
The purpose of this sound production has been pondered since Darwin observed the behaviors during his famous voyage of the Beagle. Darwin suggested the sounds produced were part of the courtship. Others since Darwin have put forth that the cracks are used by the butterflies in defense of territories. Current thinking is more supportive of Darwin’s original hypothesis.
The source of the sound also has been studied. Three possible means of sound production have been investigated: stridulation (such as that of crickets), percussion and mechanical. Recent research supports the mechanical basis for the cracking. By flexing the wings at a point where a vein buckles the audible crack can be produced. Not only can humans hear these cracking sounds, but they also can be detected by Cracker butterflies themselves.
The sense of hearing is uncommon among butterflies and moths. The basis of sound perception has been studied as extensively as that of sound production. A highly innervated organ can be found near the forewing base in Hamadryas spp. Studies have demonstrated response in this organ to the sounds produced by these butterflies. It has been speculated that this organ is a remnant of an organ found in ancestral moths, which is used to detect bat sounds.
However the cracks are produced and heard by the butterflies, they add another intriguing dimension to the butterfly exhibit. Species that can be seen in addition to the Red and Gray Crackers are the Pale, Variable, Yellow, Glaucous, Guatemalan and Starry Night Cracker at the Butterfly Wing.
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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The picture's fullsize photo is 264K. Caption: Cracker butterfly |
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