If you know how to use your eyes in your garden you may observe, some day or other, a number of curious holes in the leaves of the lilac- and rose-trees, some of them round, some of them oval, as if idle but skillful hands had been at work with the pinking-iron. In some places there is scarcely anything but the veins of the leaves left. The author of the mischief is a gray-clad Bee. For scissors, she has her jaws; for compasses, she has her eye and the pivot of her body. The pieces cut out are made into thimble-shaped bags, meant to contain the honey and the egg: the larger, oval pieces make the floor and sides; the smaller, round pieces are kept for the lid. The Leaf-cutter’s nest consists of a row of a dozen, more or less, of these thimbles, placed one on top of the other. One species of the Leaf-cutting Bee whom we will notice is called the White-girdled Leaf-cutter. She The little Bee foresees this danger. She sets to work to block the passage with a strong barricade of fragments of leaves, some dozens of pieces rolled into screws and fitting into each other. You can see that the insect has cut out these pieces carelessly and hurriedly, and on a different pattern from that of the pieces which are to make the nest. Next after the barricade of leaves comes the row of cells, usually about five or six in number. These are made of round and oval pieces, as we have seen; oval for the sides, round for the lid. There are two sizes of ovals, the larger ones for the outside and bottom of the bag; the smaller ones for the inside, to make the walls thicker and fill up the gaps. The Leaf-cutter therefore is able to use her scissors according to the task before her; she makes large or small pieces as they are needed. She is especially careful about the bottom of the bag. As The cover of the pot consists solely of round pieces, and these are cut so exactly by the careful Bee that the edges of the cover rest upon the brim of the honey-bag. No one could do better with the help of compasses. The cover of the pot consists solely of round pieces When the row of cells is finished, the entrance to the gallery must be blocked up with a safety stopper. The Bee then returns to the free and easy use of her scissor-jaws which we noticed at the beginning when she was fencing off the back part of the Earthworm’s too-deep burrow; she cuts out of the foliage irregular pieces of different shapes and sizes; and with all these pieces, very few of which fit at all Let us leave the Leaf-cutter to finish laying her eggs, and consider for a moment her skill as a cutter. What model does she use, when cutting her neat ovals out of the delicate Robinia-leaves, which she uses for her cells? What pattern that she carries in her mind guides her scissors? What system of measurement tells her the correct size? One would like to picture the insect as a living pair of compasses, able to trace curves by swaying her body, even as our arm traces a circle by swinging from the shoulder. This explanation might do if she made only one size of oval; but she makes two, large and small. A pair of compasses which changes its radius of its own accord and alters the curve according to the plan before it appears to me an instrument somewhat difficult to believe in. Besides, the Bee cuts out round pieces also. These rounds, for the most part, fit the mouth of her jar almost exactly. When the cell is finished, the Bee flies hundreds of yards away to make the lid. She arrives at the leaf from which the round pieces are to be cut. What picture, what recollection has she of the pot to be covered? Why, none at all; she has never seen it; she does her work underground, in utter darkness! At the utmost, she can only remember how it felt. And yet the circular piece to be cut out must be of a certain size: if it were too large, it would not One winter evening, as we were sitting round the fire, whose cheerful blaze unloosed our tongues, I put the problem of the Leaf-cutter to my family: “Among your kitchen utensils,” I said, “you have a pot in daily use; but it has lost its lid, which was knocked over and broken by the cat playing on the shelves. To-morrow is market-day and one of you will be going to Orange to buy the week’s provisions. Would she undertake, without a measure of any kind, with the sole aid of memory, which we would allow her to refresh by a careful examination of the object before starting, to bring back exactly what the pot wants, a lid neither too large nor too small, in short, the same size as the top?” It was admitted with one accord that nobody would accept such a commission without taking a measure with her, or at least a bit of string giving the width. Our memory for sizes is not accurate enough. She would come back from the town with something that “might do”; and it would be the merest chance if this turned out to be the right size. “What pattern that she carries in her mind guides her scissors?” Well, the Leaf-cutting Bee is even less well off than ourselves. She has no mental picture of her pot, because she has never seen it; she is not able to The insect excels us in practical geometry. I look upon the Leaf-cutter’s pot and lid as an addition to the many other marvels of instinct that cannot be explained by mechanics; I submit it to the consideration of science; and I pass on. |