The animal kingdom is divided into two subkingdoms, invertebrate and vertebrate animals -- animals with back-bones and animals without backbones. The invertebrate group is distinguished by nine phyla, or divisions. In this group there are over 500,000 known kinds of animals, ranging from the lowest form of animal life, minute single-celled protozoa, to arthropoda -- crabs, insects and spiders. In the vertebrate group there are well over 30,000 known kinds -- fishes, amphibians, reptiles, birds and mammals.
When it is stated that in this vast array of creatures the lowly, segmented earthworm is probably the most important to mankind, most may find that illogical and unreasonable. Yet, few creatures equal the burrowing earthworm as being essential to better health and greater growth to plant and vegetable life. Therefore, indirectly, it is of the utmost importance to man.
The burrowing earthworm is Nature's plow, chemist, cultivator, fertilizer, distributor of plant food. In every way, the earthworm surpasses anything man has yet invented to plow, cultivate or fertilize the soil.
While it is unquestionably true that plants and vegetables grow and reproduce their kind without the aid of the earthworm, most naturalists claim that all fertile areas have, at one time or another, passed through the bodies of earthworms.
It is also true that the finest plants and vegetables become healthier and more productive through the activities of this lowly animal, which the ordinary person considers useful only as bird food or fish bait.
The earthworm has been playing a very important role in the drama of plant life from time so distant that scientists can merely guess as to the age of this invertebrate animal. Regardless, scientific men are agreed that mankind may rightly acknowledge the earthworm as one of his best friends.
In this chapter, or lesson, the reader will be presented with a brief genealogical background of the earthworm and the manner in which it has indirectly aided mankind by directly aiding plant life. This background should help the reader to understand facts regarding the earthworm which should be known to anyone interested in gardening, farming, orcharding or poultry raising.
If must first be realized that there are worms and 'worms.' All are invertebrate animals. This work shall be focused on only the phylum annelida.
The division of invertebrate animals, of which the earthworm is a member, is composed of five families or classes. These, in turn, are divided into two orders. The phylum annelida, the entire division of earthworms, contains upward of eleven hundred species.
Of this extensive array, we shall concern ourselves only with earthworms, for there are marine worms, swamp worms and beach worms, many of which appear to be 'just worms.'
While all annelida are, more or less, closely related, each specie has distinct features. Some have habits quite foreign to other species. Some prosper only in certain, specific environments and die if transplanted elsewhere. Some have definitely formed heads, with whiskers, teeth and eyes. Others have no heads, are toothless and eyeless. Some worms are hermaphroditical, others bisexual. Some live exclusively in water, others in soggy soil, others in decayed animal matter (manure), others in decayed vegetable matter (humus).
Low as earthworms are in the scale of life, they show unmistakable signs of intelligence. Charles Darwin's experimentations with them conclusively proved that instinct alone could not guide them so consistently. (See Darwin's famous work, The Formation of Vegetable Mould Through the Actions of Worms, with Observations on Their Habits.)
Some earthworms come to the surface of the soil and can crawl a great distance, especially in rainy weather, when their burrows or tunnels are flooded. All throw their bodily excrements, technically known as castings, behind them. Some species throw their castings above the surface of the soil, forming small hillocks or mounds.
Countless thousands of years before the rocky surface of the earth disintegrated to form what we call soil, an extensive list of animals and plants lived in the waters. Marine worms were undoubtedly present in those obscure ages.
In time, as the waters receded, various animals and plants evolved certain anatomical organs to meet the new conditions. Some marine worms acquired physical characteristics which permitted them to live, first in very marshy ground, later in 'dry land.'
The phrase, 'dry land' should here be qualified, for, in the strictest sense, there are exceptionally few spots on the face of the earth that are dry. No creature can live on, or in, dry land. It is a common remark, -- breathe air -- but what we are actually doing -- "what all living things are doing -- is breathing nitrogen dissolved in water.
We should keep this fact regarding the vital need of water constantly before us as we study the worm and its relation to plant life, for both must have moisture to live.
Now that we have cursorily traced the earthworm from its parent environment to the so-called dry land, we will focus on those known to science as Oligochaeta.
This group is composed chiefly of terrestrial worms, and is the subject of the book Friend Earthworm.
The earthworms, like all other families, is sub-divided into various groups, but for our purpose all we need know are the common names for this class. These are orchard worm, rain worm, angle worm, dew worm, brandling, compost worm, night crawler, fish worm, night lions and similarly descriptive names familiar to certain areas of the United States.
Let us now combine all these common names and visualize the last earthworm we saw.
In size, it may have been from two inches to perhaps a foot in length. Although, twelve inches is long for an earthworm on the North American Continent, except in very damp forest lands.
In considering an external description of the earthworm, we find all species so much alike that few can distinguish one species from another without careful examination.
All are 'headless,' eyeless and toothless. There are no external antennae or feelers. From tip to tail the body is composed of ringlike segments. A short distance from the 'head' is seen a band, which is lighter in color than the rest of the body.
That, briefly, describes how the earthworm appears to the naked eye. The earthworm's internal system is highly complicated. Yet, paradoxically enough, it is magnificently simple. Picture a flexible metal tube the size of a lead pencil, in which is built a plant capable of refining gasoline from crude oil. In a comparative sense, the earthworm's system does to soil what the modern refinery does to crude oil.
The earthworm has a multiple system of hearts, minute tubes circling that part of the alimentary canal between the pharynx and the crop. Through a complicated system, these hearts supply blood to all parts of the body.
Minus lungs, the earthworm 'breathes' through its moist epidermis or outer skin. The blood corpuscles are colorless and float to the surface of each segment where they absorb oxygen.
Under an ordinary magnifying glass, the pores of the various segments are visible. If one were to gently squeeze an earthworm, minute drops of yellowish serum would be seen coming out from it.
This serum is composed chiefly of oil of high medicinal value. Experiments for its extraction, discussed in a later chapter, are now in progress. It is hoped that this oil may be extracted in quantities sufficient to encourage production.
Except for a number of hearts, all the vital organs of the earthworm are under the previously mentioned band, which zoologists call the clitellum. This band is the chief characteristic of the earthworm, distinguishing it from all other worms except a few leeches and a few other marine worms.
Under this band, in compact uniformity, are seminal vesicles and receptacles, testes, ovaries, oviduct and egg sac. Directly behind these is the crop, where the food is held until the gizzard, just beyond the crop, is ready to accept it. Next follows the intestine, a distinctly oval shaped tube, and then the rest of the alimentary canal to the vent or anus.
Our earthworm is bisexual, containing both male and female organs of procreation, and must perform a reciprocal act of copulation to fertilize and be fertilized.
The sexual act of the earthworm, usually occurring in the cool hours of the early dawn and twilight, makes an interesting and curious study of nature's method for propagating the specie.
Neither animal has external sexual organs, though the pores, through which the seminal fluids appear, are visible under a small magnifying glass. The sexual act is not preceded by any display of amorous cooing or lovemaking. The worms, driven solely by instinct when the procreative glands demand relief, seek a position that brings their bands together and remain thus, quite motionless, for as long as fifteen minutes. If exposed to a bright light during the sexual act, the embrace is broken. Worms, though sightless, are very susceptible to light.
During the act of coitus, each worm exchanges male sperm, impregnating, or, at least, theoretically impregnating, their female ovas. Also during the act, there is an increased flow of the fluid which keeps the entire length of the worm's body moist. This fluid forms the capsule in which the eggs are deposited. It is heavier and thickens rapidly.
When the hymeneal act is completed and the earthworms separate, this fluid forms an outer band. The new band or shield begins to move forward, eventually dropping from the earthworm's 'head.'
During the forward movement of the gelatine-like band, the impregnated eggs are held firmly within. As it drops off the earthworm, it closes into a yellowish-green pellet or capsule, slightly larger than a grain of rice. This capsule resembles, to a remarkable degree, a very small currant.
Earthworm capsules examined under a powerful microscope show a lack of uniformity in the number of cells. There will be, however, from three to fifteen fertile eggs in a capsule.
Earthworm eggs hatch in about 21 days. The newborn appear as short bits of whitish thread about one-quarter of an inch in length. In 12 to 48 hours, they become darker but are visible to the untrained eye only after a painstaking search for them.
Once hatched, it is a case of each worm for itself. Close observation seems to lead students of these lowly organized creatures to believe their mortality rate exceptionally low.
Worms begin to mate from 60 to 100 days after birth, depending upon the richness or poorness of the soil in which they live or in which they are cultured.
Mating follows at periods from six to eight days. If we are to follow the average fertility of each capsule laid, that is, three worms, one mature worm will beget over one hundred and fifty worms each year of its life. Each mating, should produce twice that number, or over three hundred worms a year.
Certain species of earthworms, particularly those that come to the surface and crawl about during wet or rainy weather, seem to be chiefly active during the nocturnal hours. Other species -- which we will discuss later -- are, apparently, active throughout most of the day and night. This species seldom, if ever, comes to the surface, depending on the porosity of the soil.
Except in highly porous soils, the earthworm must eat its way through. Having no teeth, everything before it, if not too large to swallow, is sucked into the mouth. It is a ravenous eater.
Every morsel of soil and decayed vegetable and animal matter taken in by the earthworm passes through its digestive system. This is equipped with a gizzard-like organ. Here the food value in the swallowed matter is extracted for use by the worm. The rest is carried by muscular action down through, and out of, the alimentary canal. This waste matter is called castings.
