[LETTER XXIV.]
ON THE NOISES PRODUCED BY INSECTS.
That insects, though they fill the air with a variety of sounds, have no voice, may seem to you a paradox, and you may be tempted to exclaim with the Roman naturalist, What, amidst this incessant diurnal hum of bees; this evening boom of beetles; this nocturnal buz of gnats; this merry chirp of crickets and grasshoppers; this deafening drum of Cicadæ, have insects no voice! If by voice we understand sounds produced by the air expelled from the lungs, which, passing through the larynx, is modified by the tongue, and emitted from the mouth,—it is even so. For no insect, like the larger animals, uses its mouth for utterance of any kind: in this respect they are all perfectly mute; and though incessantly noisy, are everlastingly silent. Of this fact the Stagyrite was not ignorant, since, denying them a voice, he attributes the sounds emitted by insects to another cause. But if we feel disposed to give a larger extent to this word; if we are of opinion that all sounds, however produced, by means of which animals determine those of their own species to certain actions, merit the name of voice; then I will grant that insects have a voice. But, decide this question as we will, we all know that by some means or other, at certain seasons and on various occasions, these little creatures make a great din in the world. I must therefore now bespeak your attention to this department of their history.
In discussing this subject, I shall consider the noises insects emit—during their motions—when they are feeding, or otherwise employed—when they are calling or commanding—or when they are under the influence of the passions; of fear, of anger, of sorrow, joy, or love.
The only kind of locomotion during which these animals produce sounds, is flying: for though the hill-ants (Formica rufa), as I formerly observed[600], make a rustling noise with their feet when walking over dry leaves, I know of no other insect the tread of which is accompanied by sound—except indeed the flea, whose steps, a lady assures me, she always hears when it paces over her night-cap, and that it clicks as if it was walking in pattens! That the flight of numbers of insects is attended by a humming or booming is known to almost every one; but that the great majority move through the air in silence, has not perhaps been so often observed. Generally speaking, those that fly with the most force and rapidity, and with wings seemingly motionless, make the most noise; while those that fly gently and leisurely, and visibly fan the air with their wings, yield little or no sound.
Amongst the beetle tribes (Coleoptera), none is more noticed, or more celebrated for "wheeling its droning flight," than the common dung-chafer (Geotrupes stercorarius) and its affinities. Linné affirms—but the prognostic sometimes fails—that when these insects fly in numbers, it indicates a subsequent fine day[601]. The truth is, they only fly in fine weather. Mr. White has remarked, that in the dusk of the evening beetles begin to buz, and that partridges begin to call exactly at the same time[602]. The common cock chafer, and that which appears at the summer solstice (Melolontha vulgaris and Amphimalla solstitialis), when they hover over the summits of trees in numbers, produce a hum somewhat resembling that of bees swarming. Perhaps some insect of this kind may occasion the humming in the air mentioned by Mr. White, and which you and I have often heard in other places. "There is," says he, "a natural occurrence to be met with in the highest part of our down on the hot summer days, which always amuses me much, without giving me any satisfaction with respect to the cause of it;—and that is a loud audible humming of bees in the air, though not one insect is to be seen.—Any person would suppose that a large swarm of bees was in motion, and playing about over his head[603]."
"Resounds the living surface of the ground—
Nor undelightful is the ceaseless hum
To him who muses through the woods at noon,
Or drowsy shepherd as he lies reclined."
The hotter the weather, the higher insects will soar; and it is not improbable that the sound produced by numbers may be heard, when those that produce it are out of sight.—The burying-beetle (Necrophorus Vespillo), whose singular history[604] so much amused you, as well as Cicindela sylvatica of the same order, flies likewise, as I have more than once witnessed, with a considerable hum.