Year: 1878

/ The old naturalists generally thought
that the buzzing of insects was produced
by the vibration Of the wings; but they
had scarcely attempted to. analyze the
phenomenon, and their opinion was
abandoned when Reaumur showed that
when the wings are cut blow fly con-
tinued to buzz. Other explanations of
the phenomenon have been advanced


by various naturalists, but none of
them are satisfactory. M. Jousset de


Bellesme has been making some inyesti-
cations on the subject, and, after prov
| ing that previous theories are unsatis-
factory, he describes the results of his
own researches. To avoid confusion, it


should be distinctly understood what is


meantby buzzing. In the scientific ac-
ceptation it means to initiate the


sound of the humblebee, which is the
| type of insects. But the humblebee


gives out two very different sounds,


which are an octave of each other-a


grave sound when it flies, and sharp
sound when it alights. We say, then,


that buzzing is the faculty Of insects to


produce two sounds at an octave. The


definition limits the phenomenon to
the hymenoptera and the diptera. The


coleoptera often produce in flying a
grave and dull sound, but they are pow


erless to emit the sharp sound; and,


consequently, do not buzz. There are


two or three ascertained facts which


will serve as guides in the Interpretation.
of the phenomenon. First, it is indis-
putable that the grave sound always
accompanies the great vibrations of the
wings, which serve for the translation
of the insect. 1t is easily seen that this
| sound commences as soon as the wings
begin to move, and that if the wings be
cut off it disappears entirely. The sharp
sound is never, on the contrary, pro-
duced during flight; it is only observed
apart from the great vibrations of the
wings when the insect alights, or when
it is held SO IS to hinder its movement,
and in that case the wing is seen to be
animated by rapid, trembling. 1t is
also produced when the wings are en-
tirely taken away. From these two re-
marks we may draw the conclusion that
| the grave sound belongs properly to the
wings; that it is caused by their move
ments of. great amplitude. There is
here no difficulty. As to the sharp
sound, it is certainly not produced by
the wings, since it survives the absence
of them. Yet the wings participate in
it and undergo particular trembling
during the production of this sound.
To discover the cause it is necessary to
| go back to the mechanism of the move
ment of the wing. 1t is known that
among nearly all insects the muscles
which serve for fight are not inserted in
the wing itself, but in the parts of the
thorsx which supportiit, and that it is
the movement of these which acts on
the wing and makes it vibrate. The
form of the thorax changes with each
movement of the wing under the in
fuence of the contraction of the
thoracic muscles. The muscular masses
intended for flight being very powerful
this vibratory movement OF the thoraz
is very intense, as may be proved by
holding one of these insects between
the fingers. But as the vibrations are
repeated two hundred or three hundred
times per second, they give rise to 8
musical sound, which is the sharp note


In fact, the air which surrounds the
thorax is setin vibration by that directly


and without the wing taking part in it


There are then two simultaneous sounds


-one produced by the vibration O.


the wings, and the o-her by th'
thoraeic vibration, the latter twice a.


rapid as the former, and therefore al
octave. This is why in flight only 1
single grave sound is heard. When tn


thorax moves alone sharp sound i


produced. This, M. de Dellesme be
| fieves, is the only explanation that cal


be given of the mode of production o.
the two sounds which constitute buzzing