68 VARIETY OF ORGANS OF SOUND AMONG BEETLES. (2) Prosternum on Mesosternum (Omaloplia (3) Elytra with rasp at the end (Curculionida; (4) Coxæ with rasp (Geotrupes, Ceratophyus). (6) Pygidium with two rasps in the middle (7) Abdomen with a grating-ridge and four grating-plates (Trox sabulosus). (8) Abdomen with two toothed ridges rubbing on cover-margin rasp (Elaphrus, Blethisa, Cychrus). (9) Elytra rubbing with under-wing rasp (Pelobius Herrmanni). (10) Wings rubbing against abdominal ringlets (Melolontha fullo). 5. Exploding sounds from the tail (Brachinus). 6. Sounds produced by the spiracles (Melolontha). Graber, moreover, has shown by a number of interesting experiments * that the power of hearing is by no means confined to those beetles which are known to produce sounds themselves. Passing on to other groups of insects, flies and gnats, besides the humming of the wings, produce sounds, like the cockchafer, through the spiracles, some of which are especially arranged for this purpose. If a fly be caught and held between the fingers, it will generally make a loud and peculiar sound. The hum of the mosquito is only too familiar to most of us. * "Die Chordotonal Sinnesorgane der Insekten," Arch. für Mic. Anat., 1882. DIPTERA-HYMENOPTERA. 69 Landois mentions that he has heard species of Eristalis and Syrphus sing while they have been sitting quietly. The dragon-flies (Libellulina) also produce a sound by means of their spiracles. Among Hymenoptera, the hum of an angry bee is proverbial. Nor must I omit to mention the piping noise made by young queen bees. It is well known that there is only one queen in a hive, and that working bees never turn their back on her; as she moves among the combs, they all turn towards her. If there has been a swarm led by the old queen, the young queen who has succeeded often makes a piping noise, first noticed by Huber, whose statements are generally recognized as correct.* While "singing' the queen assumes a particular attitude, and the other bees all lower their heads and remain motionless until she begins to move again. In the mean while, if there are any other young queens which have not yet left the cells, they answer the old one, and their notes seem to be sounds of challenge and defiance. Other bees also produce a sound by means of their spiracles quite different from the humming of their wings. Mutilla Europæa, a wingless species, related to and not unlike the ants, makes, when alarmed, a rather sharp noise by rubbing one of the abdominal rings against the other. Under these circumstances, Landois asked himself whether other genera allied to Mutilla might not possess a similar organ, and also have the power of producing sound. He first examined the genus Ponera, which, in the structure of its abdomen, nearly resembles * Huber, "Obs. sur les Abeilles; " Bevan, "On the Honey Bee;" Langstroth, "On the Honey Bee." Mutilla, and here also he found a fully developed stridulating apparatus. He then turned to the true ants, and here also he found a similar rasp-like organ in the same situation. It is indeed true that ants produce no sounds which are audible by us; still, when we find that certain allied insects do produce sounds appreciable to us by rubbing the abdominal segments one over the other, and when we find, in smaller species, an entirely similar structure, it certainly seems reasonable to conclude that these latter also do produce sounds, even though we cannot hear them. Landois describes the structure in the workers of Lasius fuliginosus as having twenty ribs in a breadth of 13 of a millimeter. In Lasius flavus I found about ten well-marked ribs, occupying a length of of an inch. Similar ridges also occur between the following segments. In the flies (Diptera) and dragon-flies (Libellulina), the four thoracic spiracles produce sounds; while in Hymenoptera, as, for instance, in the humble bee (Bombus), the abdominal spiracles are also musical. The sounds produced by the wings are constant in each species, excepting where there are (as in Bombus) individuals of very different sizes. In these the larger specimens give generally a higher note. Thus the comparatively small male of Bombus terrestris hums on A', while the large female hums a whole octave higher. There are, however, small species which give a deeper note than larger ones, on account of the wing-vibrations not being of the same number in a given time. Moreover, a tired insect produces a somewhat different note from one that is fresh, on account of the vibrations being slower. SOUNDS PRODUCED IN FLIGHT. 71 Indeed, from the note produced we can calculate the rapidity of the vibration. The slow flapping of a butterfly's wing produces no sound, but when the movements are rapid a noise is produced, which increases in shrillness with the number of vibrations. Thus the house-fly, which produces the sound of F, vibrates its wings 21,120 times in a minute, or 335 times in a second; and the bee, which makes a sound of A', as many as 26,400 times, or 440 times in a second. On the contrary, a tired bee hums on E', and therefore, according to theory, vibrates its wings only 330 times in a second. Marey has succeeded in confirming these numbers graphically. He fixed a fly so that the tip of the wing just touched a cylinder which was moved by clockwork. Each stroke of the wing caused a mark, of course very slight, but still quite perceptible, and he thus showed that there were actually 330 strokes in a second, agreeing almost exactly with the number inferred from the note produced. The sound emitted from the spiracles bears no relation to that produced by the wings. Thus, according to Landois, the wing-tone of the hive bee is A'; its "voice," if we may call it so, on the contrary, is an octave higher, and often goes to B" and C". In one of the solitary bees, Anthidium manicatum, the difference is still greater; the wing-tone is G', and the "voice " nearly two octaves higher, reaching to F". The wing-tone is constant, at least with the exceptions just alluded to. The "voice," on the contrary, appears to be to some extent under the control of the will, and thus offers another point of similarity to a true "voice." Thus a bee in the pursuit of honey hums 72 POWER OF VARYING SOUND. continually and contentedly on A', but if it is excited or angry it produces a very different note. Thus, then, the sounds of insects do not merely serve to bring the sexes together; they are not merely "love-songs," but also probably serve, like any true language, to express the feelings. Landois also describes the muscles by means of which the form of the organ, the tension of the drum, etc., is altered, and the tone thus, no doubt voluntarily, affected.* We can, indeed, only in few cases distinguish the differences thus produced; but as even we, far removed as we are in organization, habits, and sentiments, from a fly or a bee, can yet feel the difference between a contented hum and an angry buzz, it is highly improbable that their power of expressing their feelings should stop there. One can scarcely doubt but that they have thus the means of conveying other sentiments and ideas to one another. Butterflies and moths do not habitually produce any sound in flight. The texture of their wings is comparatively soft, and they are generally moved slowly. Still, they are not altogether silent. The death's-head moth (Sphinx atropos) emits a mournful cry, first noticed by Réaumur. This moth, he says, "dans le temps qu'il marche, a un cri qui a paru funébre; au moins est-il le cri d'une bonne âme de papillon, s'il gémit des malheurs qu'il annonce. "Le cri de notre papillon est assés fort et aigu; il a quelque ressemblance avec celui des souris, mais il est plus plaintif; il a quelque chose de plus lamentable. C'est surtout lorsque le papillon marche, ou qu'il se "Die Ton and Stimm Apparate der Insekten," Zeit. für Wiss. Zool., 1866. |