THE HUMMING, OR BUZZING OF INSECTS. It has been supposed by some entomologists that the hum of insects is produced by the os cillations of their wings during flight, and this supposition is strengthened by the fact that the tones are altered during the suspension of the insects in the air, and that the sound becomes more acute when the tips of the wings are removed. This hypothesis will not, how ever, bear the test of rigid investigation.
It was observed by John Hunter, " that in sects emitted sounds after their wings were cut off.* De Geerf, finding that after he had cut off the wings, winglets, and poisers, the buzzing continued, placed the insect under a microscope, and observing that the stumps of the wings were in rapid motion, he pulled them off by the roots, on which the buzzing ceased ; and hence he inferred that the sound was produced by the vibrations of the wings. But it is not surprising that insects, after such mutilation cease to emit any sound. Bur meisterI is of opinion that the sounds of some Diptera, such as Tabanus bovinus, are produced by a stream of air rapidly transmitted through the thoracic air-holes during flight. He has described and figured the mechanism of the thorax and the air-holes of the Eristalis trnaz, which is as follows : -- The aperture of the hinder air-hole is provided with a sphincter muscle, perpendicular to the inner surface of which are sixteen or eighteen horny lamellae, of the same breadth as the muscle, and connected in the middle by another longitudinal horny band. The sphincter muscle is lined with a membrane clothed with feathery hairs, which cover the air-hole like a sieve, and exclude foreign bodies. He leaves it to naturalists to decide whether or not this mechanism contributes to the form ation of the sound ; adding that either way it is of little consequence, as many insects have no such lamellae. He observes that when the insect sits or crawls it breathes through the air•holes of the abdomen,but during flight through those of the thorax. He considers
the hum of insects to be in reality a whistle. The pitch of this hum is hitherto unexplained, although it is quite certain that it does not depend upon the number of the vibrations of the wings, for in a favourable light the motion of the wings of many insects, whose hum is of a high pitch, can be clearly detected ; but, if that pitch were owing to the vibrations of the wings, their number would necessarily be so great as to render the motion imperceptible.* The author has recently examined, with Professor Queekett, the spiracles of other insects, such as the blue-bottle fly, and the humble bee, and has discovered in them a beautifully organised valvular opening, capable of producing the sounds which these insects emit during flight. fi In fig. 922. is shown one of the large thoracic spiracles of a blow fly (Musca vonzitoria); it consists of two valves, one much larger than the other, each being provided with numerous branching horny filaments or hairs which serve as a support to the thin membrane forming the valve ; a somewhat similar form of spiracle occurs in the humble bee, (fig. 923). The valves are nearly of equal size, and the branching hairs are much stronger and more numerous than those in the blow fly.
Besides stridulation, and humming, some insects, such as bees, emit a cry, or, as the French entomologists term it, pia:dement. M. Goureau supposes this variety of voice to be used, when bees swarm preparatory to their emigration. He remarks that those insects which produce the sound by friction are not singers, but musicians ; and that insects in general make use of their voices to communi cate certain ideas and sensations.