Worms make their burrows in a very odd manner, for they actually eat their way down into the ground, swallowing mouthful after mouthful of earth until their bodies can contain no more. Meanwhile they have been absorbing nourishment from this soil; but presently they come up to the surface and pour out the mold which they have swallowed in the form of what we call a worm-cast, after which they go down again and swallow more, and so on until the burrow is sufficiently deep.
You will be surprised, we think, to hear how much earth is swallowed by the worms in this way. Just think of it. Every year, in every acre of agricultural land all over the country, worms bring up from below, on an average, and spread over the surface in the form of worm-casts, no less than fourteen tons of earth, or about seven large cartloads!
This is why worms are such useful creatures. They are always, as it were, digging and plowing the soil. After a time the earth at the surface becomes exhausted. Nearly all the nourishment is sucked out of it by the roots of the plants. But the worms are always bringing up fresh, rich, unused soil from below, and spreading it over the surface in the form of what farmers call a top-dressing. They are doing, in fact, exactly what we do when we dig our gardens or plow our fields—burying the used-up soil that it may rest, and bringing up fresh mold to take its place.
But, besides turning the soil over, they manure it; for almost every night from early spring to late autumn worms are busy dragging down leaves into their burrows. With some of these leaves they line their tunnels, with some they close the entrances, and on some they feed. And most of them decay before very long and turn into leaf-mold, which is just about the very best manure that there is. So you see, the worms do not merely turn the soil over, they enrich it as well, and help very largely indeed to keep it in such a condition that plants can continue to grow in it.
The Lugworm
The similar lugworm lives in sandy mud on the sea-shore; and when the tide is out you may often see its casts in thousands. It is very largely used by fishermen as bait. When it is carefully washed it is really quite a handsome creature, for sometimes it is deep crimson in color, and sometimes dark green, while on its back are twenty-six little scarlet tufts, arranged in pairs, which are really the gills by which the worm breathes.
The burrows of the lugworm are not quite like those of the earthworm, for as its tunnels through the sand it pours out a kind of glue-like liquid, which very soon hardens and lines the walls, so as to form a kind of tube and prevent the sides from falling in.
The Terebella
This worm forms very much stronger tubes. It is common on many parts of our coasts. But it is not very easily found, for at the slightest alarm it retreats to the very bottom of its burrow, which nearly always runs under large stones and rocks.
The terebella makes its tube by means of the little feelers, or tentacles, which spring from the front part of its body. These have a most wonderful power of grasp, and one after another little grains of sand are seized by them, and carefully arranged in position. And when the tube is quite finished, the animal constructs a little tuft of sandy threads, so to speak, round the entrance, which you may often see in the pools left among the rocks by the retreating tide.