Page:Popular Science Monthly Volume 51.djvu/847

Rh while the sale of the polished shells as curiosities gives employment to many persons. From the whelks a dye is obtained; sepia comes from the cuttlefish or squid; while one species provides the cuttlefish bone of commerce. The smallest worm, which Shakespeare tells us, "will turn, being trodden on," has its place in the economy of life. The phosphorescent worms add to the splendors of the festivals of the nights along our shores, and are among the illuminators of the ocean; as bait they have a relation to the fisheries; leeches have a medicinal value, while the common earthworm is a valuable ally of the farmer. Darwin estimates that there are one hundred thousand earthworms in the upper six feet of every acre of ground in favorable localities, and in New Zealand three hundred thousand. They are continually turning over the soil, dragging down seeds and leaves, and bringing to the surface in some places ten tons of mold to the acre every year, thus performing a valuable service to the agriculturist.

The crustaceans are among the important scavengers of the sea and are also valuable as food for fishes. The collection of crabs, shrimps, and lobsters forms large industries all over the world, contributing directly to the support of man. In Delaware the horseshoe crab is used as guano, while the collection of fossil crabs, as trilobites, is a peculiar industry. The fresh-water cray-fish produces a concretion used as an antacid, well known to chemists. We owe many of the beauties of our summer fields to insects, all of which have their special functions and use. Even the persecuted flea may render man a service by keeping the drowsy watch dog awake, while the mosquito in tropical countries may aid in preventing the human inhabitants from living a continual siesta.

The flies are among the most valuable insect scavengers. The spiders prey upon flies, holding them in check. The silk of the spider is used as a cross line in astronomical instruments, and that of a Bermuda species as sewing silk. Bridge makers have obtained valuable suggestions from these silent workers, from whose web one of the kings of France is said to have made a coat. Grasshoppers and locusts are enemies of civilized man, but are eaten by the Indians, while in the Malay country the dragon fly is considered a delicacy.

The cochineal produces the famous commercial dye, a valuable industry. Manna comes from the puncture of an allied insect, while another insect produces wax. A popular eye powder among the Chinese is made from a fly. The silk industry in the United States, the product of the silkworm, represents a capital of twenty-seven million dollars, and the moths and butterflies perform an equally valuable work in fertilizing flowers, thus insuring the crops. A decoction of oak and other galls of the gall