The Common Objects of the Country

by J. G. Wood

There are many kinds of leaf-rollers, each employing a different mode of rolling the leaf, but in all cases the leaf is held in position by the silken threads spun by the caterpillar.

Some use three or four leaves to make one habitation, by binding them together by their edges. Some take a single leaf, and, fastening silken cords to its edges, gradually contract them, until the edges are brought together and there held. Some, not so ambitious in their tastes, content themselves with a portion of a leaf, snipping out the parts that they require and rolling it round.

The insect before us, however, requires an entire leaf for its habitation, and there lies in tolerable security from enemies. There are plenty of birds about the trees, and they know well enough that within the circled leaves little caterpillars reside. But they do not find that they can always make a meal on the caterpillars, and for the following reason.

The curled leaf is like a tube open on both ends, the caterpillar lying snugly in the interior. So, when the bird puts its beak into one end of the tube, the caterpillar tumbles out at the other, and lets itself drop to the distance of some feet, supporting itself by a silken thread that it spins.

The bird finds that its prey has escaped, and not having sufficient inductive reason to trace the silken thread and so find the caterpillar, goes off to try its fortune elsewhere. The danger being over, the caterpillar ascends its silken ladder, and quietly regains possession of its home.

Myriads of these rolled leaves may be found on the oak trees, and the caterpillars may be driven out in numbers by a sharp jar given to a branch. It is quite amusing to see the simultaneous descent of some hundred caterpillars, each swaying in the breeze at the end of the line, and occasionally dropping another foot or so, as if dissatisfied with its position.

Each caterpillar consumes about three or four leaves in the whole of its existence, and literally eats itself out of house and home. But when it has eaten one house, it only has to walk a few steps to find the materials of another, and in a very short time it is newly lodged and boarded.

The perfect insect is called the “Green Oak Moth”. The colour of its two upper wings is a bright apple green; and as the creature generally sits with its wings closed over its back, it harmonises so perfectly with the green oak leaves, that even an accustomed eye fails to perceive it. So numerous are these little moths, that their progeny would shortly devastate a forest, were they not subject to the attacks of another insect. This insect is a little fly of a shape something resembling that of a large gnat; and which has, as far as I know, no English name. Its scientific title is Empis. There are several species of this useful fly, one attaining some size; but the one that claims our notice just at present is the little empis, scientifically Empis Tessellata.

I well remember how much I was struck with the discovery that the empis preyed on the little oak moths, and the manner in which they did so.

One summer’s day, I was entomologising in a wood, when a curious kind of insect caught my attention. I could make nothing of it, for it was partly green, like a butterfly or moth, and partly glittering like a fly, and had passed out of reach before it could be approached. On walking to the spot whence it had come, I found many of the same creatures flying about, and apparently enjoying themselves very much.