The trunk is placed exactly between the two eyes. As long as the butterfly does not want to take nourishment, the trunk remains rolled in a spiral. Some are so short, that they scarcely make one turn and a half or two turns; some larger sized make three turns and a half or four turns; lastly, some very long are curled as many as eight or ten times.
This is how the butterfly makes use of its trunk: When fluttering around a flower, it will very soon settle on or quite close to it. The trunk is then brought forward entirely or almost entirely unrolled; very soon afterwards it is almost straightened, then directed downwards, and plunged into the flower. Sometimes the insect draws it out a moment after, curves it, twists it a little, and sometimes even curls it partially up. Immediately it straightens it again, to plunge it a second time into the same flower. It repeats the same manœuvre seven or eight times, and then flies on to another flower.
Fig. 137.—Antennæ of Lepidoptera.
This trunk, of which the butterfly makes such good use, is composed of two filaments more or less long, horny, concave in their interior surfaces, and fastened together by their edges. When cut transversely, one sees, according to Réaumur, [47] that the interior is composed of three small rings. Consequently, there are three canals in the trunk: one central, the other two lateral ([Fig. 138]). Are all these three used to conduct the juice of flowers into the butterfly's body? Réaumur has made some very interesting observations on this subject, by observing a moth which was sucking a lump of sugar whilst its portrait was being taken.
Fig. 138.
Section of a Butterfly's Trunk, after Réaumur.
"I held in one hand," says Réaumur, "a powerful magnifying glass, which I brought near to that part of the trunk I wished to examine; I was sometimes half a minute, or nearly a minute, without perceiving anything, after which I saw clearly a little column of liquid mounting quickly along the whole length of the trunk. Often this column appeared to be intersected by little balls, which seemed to be globules of air which had been drawn up with the liquid.