In our own country and in most parts of the world there are large grubs or caterpillars, such as those of the goat moth, three inches long and as thick as one’s finger, which eat into the stems of trees and spoil the timber. The grub of the handsome moth known as the wood leopard is another of these. It attacks poplar trees, and we used to take it in numbers in the London parks and squares when I was a collector. The goat moth is specially destructive to willow trees. But there are a very large series of smaller grubs and adult insects which injure trees or bore or devour wood already cut and dried. Among these are the saw-flies and a number of beetles, and in Sicily and the tropics there are the wonderful white ants which are not ants at all, but more like May-flies. The destruction caused by these borers and eaters of wood is increased by the fact that when they have riddled a piece of wood, moisture penetrates it, and vegetable “moulds” flourish within it and complete the break-up. Among the most destructive borers of wood are those which attack the ships and piers of wood placed by man in the sea. These are certain shell-fish, called ship-worms (_Teredo_), which are really peculiarly modified mussels. There is also a tiny shrimp-like creature, the _Limnoria terebrans_, which does enormous damage by its borings to piers of wood erected in the sea. True insects do not flourish in the sea. There are marine bivalve shell-fish which bore into clay, sandstone, chalk, and even into hard granite-like rock. They do not use jaws or teeth for this purpose, but the surface of their shells, which are sharp and spiny, and also the sand which adheres to their soft muscular bodies like emery powder to the pewter-plate of a lapidary’s wheel. You may see the large and small holes made by _Pholas_ (called also “the piddock”) and other bivalve shell-fish in the clay and chalk rocks of the seashore on most parts of the English coast. Most boring animals swallow the material which they excavate in the act of boring, just as the earth-worm swallows the soil into which it bores, and as many sand-worms do, throwing out from the hind end of the body, in the form of a little coiled-up heap, a vast quantity of undigested matter which has passed through them. But many insects which swallow some of the material disengaged by their jaws remove, in addition, a large quantity which is ejected from the boring as powder, like sawdust, and others do not swallow any of the material into which they bore. So, too, the _Pholas_ and marine-boring mussels do not swallow the material which they loosen. It is a very slow process, the boring in rock, and the fine particles rubbed away by incessant movement are carried off in the sea-water.