Richard Sterling, age 13, of Haggerstown, Md., for his question:
HOW LONG CAN AN EARTHWORM GROW?
An earthworm, which is also called a night crawler, is a common worm that is found in moist, warm soil in many parts of the world. Earthworms range in size from those that are just a fraction of an inch in length to those that are up to 11 feet long.
Earthworms have smooth bodies that are made up of rings called annuli. They are cylindrically shaped and they taper off at both ends. Minute bristles called setae project from the body.
Although a difference in shading exists between the upper and under surfaces and between different parts of the body, earthworms in general are uniform in color, usually pale red, but varying from dull pink to brown.
Earthworms play an important role in soil ecology. By being continually loosened, stirred up and aerated by the action of, soil is made more fertile. Earthworms also form a source of food for many animals, constituting the principal food of moles and shrews.
Earthworms must live in moist soil containing organic matter. They usually live in the upper layers of the soil, but in winter they penetrate more deeply to escape frost. During unusually hot weather they also penetrate downward to avoid dehydration.
Earthworms shun daylight but frequently come to the surface of the soil at night to feed and to throw off their castings. In the daytime they appear upon the surface of the soil only under unusual conditions, such as the flooding of their burrows by excessive rainfall.
It might be hard to believe, but earthworms are capable of burrowing with considerable speed, especially in loose soil. The bristles along the sides of the body are of great assistance in their movements. In burrowing, earthworms swallow large quantities of earth that often contain vegetable remains. They are able to digest the nutritive matter of the soil.
The muscular system of the earthworm is made up of an outer series of circular or traverse muscle fibers that girdle the body and an inner series of longitudinal muscle fibers employed in moving the setae.
The circulatory system consists of a prominent dorsal blood vessel and at least four ventral blood vessels, running longitudinally in the body and connected with one another by a regularly arranged series of traverse vessels. The dorsal vessel is provided with valves and is the true heart. Most of the pumping of blood, however, is performed by general muscular movements.
The central nervous system consists of a pair of suprapharyngeal ganglia, which is often called the brain, and ventral cord that lies beneath the alimentary canal and bears ganglia in every segment. Earthworms have no sense organs other than those of touch.
A worm's digestive system consists of a muscular pharynx, a slender esophagus, a thin walled crop or food receptacle, a muscular gizzard used for grinding ingested earth and a long, straight intestine