A Device for Measuring the Flexural Stiffness of Insect Wings, or How to Make a Wing-Bar Gizmo

Abstract

Flexural stiffness is an important property of many biological structures, including insect wings, but measuring it can prove challenging when the structures to be measured are small and light or have a low elastic modulus. We have designed, constructed, and tested a rugged and inexpensive device for measuring flexural stiffness. The apparatus was validated by testing with fine gage copper wire and comparing our results with those obtained from standard test equipment used for tensile testing. It is shown that results can be obtained with the wings of small butterflies. Preliminary findings on Strymon melinus (Hübner), the Gray Hairstreak, showed that the stiffness measurements of the butterfly wings were repeatable and therefore the testing mechanism was not damaging the wings. Little variation was found between the dorsal and ventral direction in the experimental measurements. The stiffness tester provides a simple, low cost, means to measure the flexural stiffness of small and light biological structures. This device is well within reach, and provides a means, of quality research in a small college or university setting.