HOW BUTTERFLIES HEAR

Evening Star, Issue 17542, 23 December 1920, Page 10

HOW BUTTERFLIES HEAR

In recent years numerous interesting experiments have been made in regard to the sensory organs of insects. In the latest volume, No. 41, of ‘The Zoological Year Book’ (in German), published in Berlin, there are reported the results of an extremely extensive study made by Mr F. Eggers, concerning the organs of hearing of gome of the butterflies,, the spiders, and the moths. These possess certain structures in the last ring of the thorax, which have hitherto escaped notice, and whose' true significance has been ignored. It now appears that this structure is a socalled tympanal organ, similar to that possessed by crickets and grasshoppers, but much more delicately constructed. The essential part of this organ is an airfilled, tracheau vesicle or “bladder” (such as is possessed by many winged insects and by some butterflies), which lies very close to two extremely thin portions of the external covering of chitin; these two attenuated portions of the chitin are known as the true drumhead and the opposite drumhead. The “true” drumhead is so called because It is connected with the delicate nervous apparatus designed to receive the vibration of sound waves; the opposite drumhead is not thus provided and probably acts merely as a sort of sounding-board to re-enforce the vibrations. The nerve apparatus itself consists of a strand of connected cells at tacbed to the elastically vibrating drumhead ; this strand of cells contains two sensory cells whoso most delicate projections end in the so-called “ peg,” which is characteristic of what is known as the chordo-tonal organs. That the insect distinguishes sounds through the tympanal organ has been satisfactorily proved by experiments with crickets, since it has been found that tho well-known chirping sound uttered by the male attracts only those females in possession of this organ, whereas, when it was destroyed, the female was incapable of perceiving the ardent serenade of a would-be wooer. It is reasonable to conclude that the very similar but more delicate organ in butterflies has a similar function, though we cannot test the matter in the same manner, but it seems certain that many butterflies are affected by high, shrill tones, such as that made by a rubbing of a cork against a wet glass, and that in the Endorsa aurita the female answers a clattering sound made by the male with a fluttering motion of the body and wings. In general, it seems •especially the males which are provided with a chirping apparatus. But while the production of sound is thus shown to be connected with the mating instinct and to form a means of courtship, this function is also assisted by sight and smell. An unexpected discovery is that organs of hearing are more frequently found in butterflies that fly by day than in those that fly by night.