Each individual of the earthworm family is both male and female (hermaphrodite), having both eggs and spermatozoa, but it is not self-fertilizing. An act of copulation is necessary in order that the eggs may become fertile. Situated back from the head about one-third the length of the worm is the "clitellum," a band of tissue surrounding the body. The Century Dictionary gives a very good definition of the clitellum. We quote in part: " . . . the saddle of an annelid, as the earthworm; a peculiar glandular ring around the body, resulting from the swelling and other modification of certain segments. It is a sexual organ, producing a tough, viscid secretion by which two worms are bound together in a kind of copulation." The clitellum is easily identified, as it stands out above the surface of the body as a distinct band, darker in color than the rest of the body.
In a bulletin titled, The Earthworms of Ohio, issued by the Ohio Biological Survey, Dr. Henry W. Olson gives a very concise and clear description of the act of copulation and the reproductive functions of earthworms. We quote in part from this description:
Each individual is a male and female (hermaphrodite), so anyone of the same species will do for a mate. Though having both eggs and spermatozoa, they are not self-fertilizing, but mutually fertilize each other's eggs...
The two worms meet and overlap one another to about one-third to one-fourth of their lengths, with the heads facing in opposite directions and the ventral sides in contact. They then secrete quantities of viscous mucus, which forms a thick band about the clitellar regions of their bodies. These mucous hands surround both bodies and serve to bind the copulating individuals tightly together. Each worm then acts as a male, giving off a quantity of seminal fluid that is conducted along the grooves to the seminal receptacles of the other, where it is picked up and stored. After the worms have separated, the slime tube which is formed by the clitellum of the worm is worked forward over the body, collecting albumen from the glands of the ventral side. As it passes over the fourteenth segment, it collects a few eggs from the oviducts and then passes the ninth and tenth segments, where it receives spermatozoa from the seminal receptacles where they have been stored up. The sperm then fertilizes the eggs. The slime tube is gradually slipped off over the head, closing up as though with a drawstring, as first its anterior end and then its posterior end slips off over the sharp prostomium.
This closed slime tube, with the fertilized eggs and nutritive fluid which it contains, constitutes the cocoon. In this cocoon the eggs develop directly into the young worms, which, when ready to emerge, crawl out through one end of the cocoon after the slime plug has been dissolved away. The cocoons vary in size and shape, according to the species. The smallest are hardly one millimeter in length, while the largest are as large as eight millimeters... In Lumbricus terrestris (commonly known as the orchard worm, rainworm, and various other popular names), the capsules are lemon-shaped, having an olive color. The number of eggs in the capsules of Helodrilus trapezoides is from three to eight; in those of Lumbricus terrestris it is from four to twenty. All of the eggs of the Lumbricus terrestris become fecundated and develop; on the other hand, in the capsules of H. trapezoides one egg only, or rarely two or three, produce embryos... The embryos escape as small worms in about two to three weeks.
Under favorable conditions, which means plenty of food, moisture, and mild summer temperature, the domesticated earthworm will produce one of the lemon-shaped egg-capsules every seven to ten days. The capsule (cocoon) may contain from two or three to as high as twenty fertile eggs. In a moist, warm environment, the incubating period is from two to three weeks.
The newborn worms first appear as whitish bits of thread, about one-quarter inch long or smaller. They gradually become darker within a few hours and within a few days can be readily identified as tiny, reddish-colored earthworms. To the untrained eye, the newborn worms are visible only after a careful search for them. Except for size, they are hatched as full-fledged earthworms and immediately begin their life-work of devouring earth with all it contains, digesting and utilizing the organic food material from the ingested earth, and finally depositing the residue on or near the surface as castings.
While the newborn worms are hard to see, there is no difficulty in identifying the egg-capsules. The color is usually radically different from that of the soil, varying from light lemon color in freshly passed capsules to a dark purple in capsules nearing maturity and ready to hatch. Size varies, depending on the size of the worm from which they come, ranging from the size of a pinhead to about the size of a grain of rice. A handful of earth from a properly prepared culture box may contain several dozen capsules.
While the normal incubating period at right temperature has been stated to be from two to three weeks, this period may be extended almost indefinitely by drying out the capsules or by refrigeration. Under ordinary conditions of temperature and moisture as found in the earth at the time the capsules are produced, they will incubate and hatch within the normal period. On the other hand, if the capsules happen to be subjected to the heat of the sun and dry out, or are dried purposely for preservation, they may remain dormant and fertile for months and then swell and develop under proper temperature and moisture. Capsules have been reported to have hatched out after lying dormant for eighteen months. Also, capsules may be placed in refrigeration at temperatures ranging from fifty degrees and lower, and thus kept dormant and fertile until they are desired
for use. In frozen ground and manure piles and frozen compost heaps, as soon as the spring thaw comes and the earth or manure warms up, great numbers of capsules which have been dormant will hatch out. This stability of the fertile eggs under many different conditions accounts for the very wide distribution of the earthworm over the earth, from the far north to the tropics, from sea level to high altitudes. Capsules become dried out and are carried great distances and scattered by the wind in new locations. They may stick to dry soil on the hoofs or hides of animals and be transported from one place to another. They are sometimes swallowed by birds and fail to digest and are then dropped in a new location, perhaps on a high mountain or on an island of the sea, or some other out-of-the-way place where it would have been impossible for a mature worm to find its way. Earthworm capsules are often transported great distances on the roots of plants and start a colony hundreds or thousands of miles from the original location. On account of this stability, it is possible to produce earthworm egg-capsules commercially and ship them to any part of the world, thus enabling people anywhere to establish intensive earthworm culture for impregnation of the earth or for other purposes.
After hatching, the young worm develops rapidly and in from sixty to ninety days will reach the reproductive stage and may begin to produce capsules. This does not mean that the worm is fully grown in this length of time, but means that the reproductive organs have reached a point of maturity where they will begin to function. The egg-capsules from these young worms may be almost microscopic in size and difficult to find. It will usually require several months to a year for a domesticated earthworm to reach full mature size, averaging about four inches in length. If desired for use as fishbait, the older worms are best.
In a favorable environment an earthworm will live for many years. One report was given of an observation carried out for a period of fifteen years and the worm under this experiment appeared just as young as ever. As a matter of fact, the earthworm is about as nearly perfect a digestive apparatus as can be conceived of in the animal world. Its secretions take care of every form of food, both acid and alkalinesugars, starches, proteins, fats. Equipped with a powerful gizzard, it does not have to select or chew the food. The worm swallows anything small enough to enter its mouth, including grains of sand and small stones which act as millstones in the gizzard, which grinds and mixes everything. It absorbs and assimilates nutrients from the swallowed material. It breathes through the skin and eliminates through the skin. So, barring accidental destruction, earthworms should enjoy comparative immortality in the flesh, remaining eternally youthful through perfect assimilation and elimination.
As earthworms are both male and female in one body, a colony may be established from one fertile earthworm or from a single egg-capsule. With a capsule being produced every seven to ten days and hatching from one or two to twenty worms, it can be seen that production will soon reach astronomical figures. Those who are particularly interested in mathematics can take a pencil and paper and figure it out. There is no difficulty or problem in the production of plenty of worms, even into the millions, once the simple technique is studied and a start made.