WHAT DO INSECTS HEAR?

Evening Star, Issue 18998, 21 July 1925, Page 8

WHAT DO INSECTS HEAR?

LITTLE RESPONSE 70 SOUND Can insects hear? Some of the insects that have a very definite purpose for detecting sound connecced with their love alfairs are endowed witli auditory powers, but this special provision does not apply to most species. Very little seems to have been discovered concerning the detection of sounds by the invertebrates; anatomically wo only know that they have no auditory apparatus like those developed by the vertebrates. Anything in the nature of a tympanum, a sense-attached disc or drum for the reception of waves of sound, seems to be peculiar to the creatures with backbones. Being comparatively diminutive, ami having a nervous construction susceptible to touch, sight, taste, and, most delicately, to smell, it would appear natural that a disturbance of the atmosphere resulting from any kind or degree of noise must ho readily detected, especially through such sensitively attached organs as tho antenmn, the palpi, tho wings, and even the legs. But with tho exception of the very evident hearing of certain families of grasshoppers, crickets, and beetles, the males of wliich call tho females by stridulating, there scorns to he no evidence, after careful observation, that the majority' of invertebrates have any sense of sound as conveyed by the atmosphere. The antennal would seem to bo fbo most likely organs of hearing. The females of katydids, true and false, of tho crickets, those of the deathwatch, and certain longicorn hectics very obsorvcdly use their long and slender antenna; in locating tho call notes of the other sex. These flexible, socalled feelers are constantly moving so as to locate the sound, and they, no doubt, guide these insects in their response to a musical or poisy serenade. This fact might also lead to the conclusion that other insects with similar antennal development should he able to detect sound, but where there are no special reasons for hearing in addition to the ever-present one of detecting tho nearness of an enemy there seems to bo no auditory development of any sort. It is difficult to locate the organs of sense in insects other than sigbt,_ and this is complicated because of tlie single ocelli and the multiplications of the discs. It is also hard to determine tho extent of these senses by observation of the sense-registering organs. Arthropods breathe through their iraclnn; it would seem that they should receive odors in the same manner as do the vertebrates, but instead they have special organs of smell. _ It is possible that these highly sensitive head attachments merely come into play to aid, through determining odors, tho far less sensitive hearing or meagre susceptibility to sound.

Experiment does more than all else to determine the factors of sense, sometimes very completely upsetting theories. There seems to be no evidence that tho delicate antonme of most insects are susceptible to sounds of any kind, because some species arc. Has Nature merely made those organs in the stridulating species suceptible to sounds and developed a minor discrimination therewith, nr perhaps made them susceptible only to certain vibrations? A female cricket will pay no attention to the stridnlution of a male of any allied species, nor will she give the slightest hood to tho scrapings of a violin, except when they are a close imitation of those made by her own species. This is the case also with the true katydid and tho larger false katydid, tho males of tho latter making a clicking sound like the striking together of small pebbles, but this sound may be closely 'imitated without tho discriminative katydids giving tho least indication that any sound is apparent to them.

. It has been claimed that the organs of hearing of the katydids and crickets are to be found in tho front logs. There is a widening of tho tibia that permits of a broadened cleft, _ within which is a sort of disc not unlike tho inner ear drum or the tympanum of a fish. But it may bo proved that these organs have little or nothing to do with receiving sound. Grasshoppers and crickets as a means of escape readily cast off a leg when that member is seized by an enemy, and this evidently causes no particular discomfort, judging by the subsequent actions of the insect. When the tiro forelegs of a caged female of the largo false katydid were separated from her she very soon resumed the quest for the ■stridulating male hidden among a tangle of twigs and leaves in the same cage, the antonme undoubtedly directing the search. Moreover, the males of certain crickets do not possess these supposed auditory appendages in the legs. But these crickets are, nevertheless, susceptible to the stridulations of other members of their own sox and species, as may he shown by their striking up in animated rivalry. It seems strange that the sensitive antenna; of butterflies and those of certain moths that possess many branched, feather-like, or hair-like feelers would not ho sensitive to the most delicate disturbances of the atmosphere and.attuned to certain sounds in order, at least, to warn them of approaching danger. But after long, frequent, and varied experiment it has not come within tho power of the writer to discover any sound-making scheme or instrument to which these or most other insects will respond.—F. A. Aaron, in ‘Scientific American.’