Earthworms are classed as an animal, even though they have no skeleton, eyes, nose, ears, hands, or legs. They sense light by special sensors. When an earthworm is exposed to light, it quickly buries itself in the ground or hides below the nearest object it finds.
Earthworms have no head but have a mouth and a brain. They have 5 connected hearts located up front behind the mouth, blood vessels, a gizzard, and intestine. The worm’s body contains 2 sets of muscles, one longitudinal and one circular.
The earthworm’s body consists of numerous segments or rings. Mature worms have 115 to 200 segments, depending on the species. Each segment has 4 pairs of tiny retractable bristles. The worm uses the bristles and muscles to propel itself and to burrow.
Earthworms have a bottom side and a top side. Their skin is slimy. The slime is vital to the earthworm’s survival for 3 reasons:
1. It acts as a lubricant which makes it easier for the worm to burrow.
2. It allows the worm to breathe through the skin (earthworms have no lungs). Oxygen from the air dissolves in the slime then enters the earthworm’s bloodstream. If the worm’s skin dries, as when the worm is exposed to the sun or when the soil becomes dry, it cannot breathe and dies shortly thereafter.
3.It holds the worms together during mating.
Lifecycle of the Earthworm
Earthworms are bisexual in that they have the organs of both male and female. They reach maturity at about 4 months old, but keep growing until they are about one year old.
A mature earthworm is distinguished by a thick band called clitellum (the c is pronounced k) that is closer to the head than to the tail. The clitellum plays an important role in the reproduction of earthworms.
Most of earthworms’ activity takes place in the top 12 inches of the soil, where organic debris is abundant. However, during extreme heat or cold, earthworms move downward. Some burrow as deep as 10 feet. In soft soils, the earthworm burrows by pushing the soil aside with its body.
The worm contracts its longitudinal muscles, which causes it to become thicker and shorter. Meanwhile, it anchors the bristles of its rear segments against the walls of the burrow. Next, it contracts its circular muscles, which propels the worm forward. In hard soils, the earthworm eats its way through. It swallows the soil in front of it, digests it, then discharges it from its rear end in the form of cast.
Night crawlers use their bristles to anchor their rear end to the mouth of the burrow while the rest of their body moves about the surface searching for food. If a bird or a person tries to pick them up, they contract their long muscles, which make them thicker, and cling to the burrow by the bristles. The strength of their grip and the sliminess of their body help them escape.
Sometimes the pull is strong enough to break the worm. If fewer than 10 segments from the front are cut off, the worm will grow replacement rings and a mouth. If up to 25% of the worm’s rear segments are cut off, new segments grow in their place. If more than these are cut off, the worm will die.
Even though earthworms have both male and female organs, they cannot fertilize their own eggs. Two worms must mate and each fertilizes the other’s eggs. When mating, both worms lie with the underside of their clitellum facing each other and their heads facing opposite directions. Mucus holds the reproductive areas together. After mating, each worm produces eggs that are fertilized by the sperms of the other.
The fertile eggs are stored in sealed lemon-shaped capsules called cocoons, each containing an average of 4 eggs. The eggs hatch only when the weather is favorable. If the soil is dry or the temperature is very hot or very cold, the eggs stay dormant in the cocoons and don’t hatch.
Where to Buy Earthworms
Earthworms are sold in commercial earthworm farms and through catalogs. Before you decide to buy earthworms, you should weigh the disadvantages.
First, the worms you are likely to buy are raised in a climate and under conditions that may be different from those in your garden.
Second, they are relatively expensive. Five hundred earthworms sound like a lot but are not a significant quantity. However, you can increase the population of earthworms in your garden by many times by adding organic material to your garden.
If you start with a soil that has no worms, which is very unlikely, some will immigrate to your garden from the surrounding area. Any land that has vegetation on it is likely to contain earthworms. The topsoil you buy may contain cocoons that will hatch when the conditions are favorable.
With ample organic material a pair of earthworms can multiply into 100 or more in a year. If your garden doesn’t have earthworms because of lack of organic matter or because of excessive acidity or alkalinity, the ones you buy will either die or move to another area.