More than 6,000 species of earthworms belonging to 20 families populate the planet. Some are more common in certain parts of the world than others. They thrive in soil, underneath objects like rocks and fallen trees, in piles of decaying leaves and in wet, vegetative areas. Earthworms are a friend to nature and gardeners because their activity, burrowing and feeding habits help improve soil.
How Earthworms Move
With no appendages to help them along other than the protrusible setae--bristles that stick out--earthworms rely on their musculature. By repeating contraction and relaxation of their body wall muscles, the earthworm extends its front forward and anchors itself in the soil with its bristles in the front. It then releases its grip in the soil at the back by retracting those bristles, and the body is pulled forward. This burrowing churns up the soil, aerating the space behind the earthworm.
How Earthworms Eat
Earthworms do not have eyes or any means of catching food. They are simply scavengers who feed on soil above ground and dead organic matter like decaying leaves. As the soil passes through their bodies, nutrients are extracted. Soil enters the mouth, is swallowed and passes through an esophagus with three glands that secrete a substance designed to rid excessive amounts of calcium from their food. When the food reaches the gizzard, tiny stones help grind the food further. Gland juices in the intestine digest the food and distribute it throughout the body. Waste products from earthworms are left on the top of the soil and are called casings.
How Earthworms Are Beneficial
The burrowing action and casings aerate the soil. When soil is aerated, plant roots have an easier time moving through it as they grow. Moisture can also reach places it cannot when soil is more compacted. The scavenging of dead organic matter from the surface adds nutrients to the surface and subsurface layers of soil when the earthworm's casings are left behind. The presence or lack of earthworms can be an indicator of soil quality.
How Earthworms Breed
All types of earthworms have both male and female attributes, making them hermaphrodites. Each can make eggs and sperm, but the eggs must be fertilized by another earthworm. Mating occurs after rain when the ground is wet. The worms join at their back ends and secrete a mucus that encloses each in a tube. Once they have transferred the sperm into each other's sperm receptacle, they separate. The worm next secretes more mucus that travels over the length of the worm, collecting eggs as it passes over the ovary and sperm as it passes the sperm receptacle. It continues moving along the worm until it slips off and closes, forming an egg cocoon. Worms develop here, eating the contents of the cocoon, much like the white of chicken egg, and burst through the membrane when they are big enough.
How Earthworms Breathe
Without lungs, earthworms must breathe through their skin. For this to work, the earthworm must remain moist at all times. Excreting a mucus and a body fluid, earthworms need damp soil to live in to sustain the making of the fluids. They have sensors that detect light and help keep them in dark places where moisture is more available. The moisture allows the thin outer skin to release and absorb gases, letting the earthworm breathe.