Leaf of the Dew-berry Bramble (Rubus cæsius), mined by Caterpillars.
Tunnels very analogous to the preceding may be found upon the common bramble (Rubus fruticosus); and on the holly, early in spring, one which is in form of an irregular whitish blotch. But in the former case, the little miner seems to proceed more regularly, always, when newly hatched, making directly for the circumference, upon or near which also the mother-moth deposits her egg, and winding along for half the extent of the leaf close upon the edge, following, in some cases, the very indentations formed by the terminating nervures.
The bramble-leaf miner seems also to differ from that of the rose-leaf, by eating the pulp both from the upper and under surface, at least the track is equally distinct above and below; yet this may arise from the different consistence of the leaf pulp, that in the rose being firm, while that of the bramble is soft and puffy.
On the leaves of the common primrose (Primula veris), as well as on the garden variety of it, the polyanthus, one of those mining caterpillars may very frequently be found. It is, however, considerably different from the preceding, for there is no black trace—no river to the valley which it excavates: its ejectamenta, being small and solid, are seen, when the leaf is dried, in little black points like grains of sand. This miner also seems more partial than the preceding to the mid-rib and its vicinity, in consequence of which its path is seldom so tortuous, and often appears at its extremity to terminate in an area comparatively extensive, arising from its recrossing its previous tracks. (J. R.)
Leaf of the Primrose (Primula veris), mined by a Caterpillar.
Swammerdam describes a mining caterpillar which he found on the leaves of the alder, though it did not, like those we have just described, excavate a winding gallery; it kept upon the same spot, and formed only an irregular area. A moth was produced from this, whose upper wings, he says, “shone and glittered most gloriously with crescents of gold, silver, and brown, surrounded by borders of delicate black.” Another area miner which he found on the leaves of willows, as many as seventeen on one leaf, producing what appeared to be rusty spots, was metamorphosed into a very minute weevil (Curculio Rhionoc.). He says he has been informed that, in warm climates, worms an inch long are found in leaves, and adds, with great simplicity, “on these many fine experiments might have been made, if the inhabitants had not laboured under the cursed thirst of gold.”[BZ]
The vine-leaf miner, when about to construct its cocoon, cuts, from the termination of its gallery, two pieces of the membrane of the leaf, deprived of their pulp, in a similar manner to the tent-makers described above, uniting them and lining them with silk. This she carries to some distance before she lays herself up to undergo her change. Her mode of walking under her burthen is peculiar, for, not contented with the security of a single thread of silk, she forms, as Bonnet says, “little mountains (monticules) of silk, from distance to distance, and seizing one of these with her teeth, drags herself forward, and makes it a scaffolding from which she can build another.”[CA] Some of the miners, however, do not leave their galleries, but undergo their transformations there, taking the precaution to mine a cell, not in the upper, but in the under surface; others only shift to another portion of the leaf.