Earthworms and Behavior

There are more than 2,700 different types of earthworms.

Earthworms are annelids, the class of worms with segmented bodies. With 2,700 different species, they form a complex and prolific group. Earthworms live mostly below the surface of the soil or under bodies of water---both salt water and fresh water---where they are safe from the dehydrating rays of the sun as well as from predators.

Anatomy

Earthworms, like snakes, have no feet or other appendages, except minuscule fibers called "setae," which are used like arms to help the worm drag itself along, increasing its momentum, or to cling to a surface. When not in use, the fibers are retracted inside of the worm's body. When a worm is under attack by a predator, setae make it more difficult to extricate.
The earthworm can manipulate the shape of its long, tubular body to adapt to the size and shape of a given hole in the soil or other fissures. According to BackyardNature.net, earthworms' "complex system of muscles enables them to not only wiggle like crazy but also to very quickly alternate between being stubby and thick, and long and slender."
The earthworm's body tapers at either end and is segmented throughout. It also has a rudimentary nervous system.

Reproduction

Though earthworms propagate through means of sexual reproduction, a singular worm contains both the eggs and the sperm required for fertilization. Still, a worm cannot fertilize its own eggs. Instead, two worms must line up side by side and share the sperm contained in their bodies. That sperm then travels through a mucus-like substance to the eggs. According to the U.S. Department of Energy, the eggs are "formed in a slime tube that slips over the worm's head and forms a cocoon or capsule that incubates them. Eggs develop into tiny worms in the cocoon and crawl out through one end when ready to emerge."

Earthworm Nutrition

Earthworms live on a diet of soil enriched with plant and animal byproducts. The digestive system of the earthworm mines the soil for these organic components and excretes the rest as waste. Earthworms thrive in soil and earth high in these extra organic amenities and are commonly found in compost bins.

Predators

Like many worms, earthworms are part of the diet of multiple predators. Fish and birds both dine on their long bodies as do other small, burrowing ground mammals. They are widely used as bait for fishing.
Partially as a means of defense, earthworms spend as much time as possible below the water or earth's surface, out of sight. The body of the earthworm, with its brown and tan hues, blends with its natural surroundings.

Earthworm Benefits

For some people, earthworms are more than an interesting backyard resident. They are their stock in trade for earthworm farmers. Earthworms may be sold to gardeners, other farmers and fishermen. In addition to being a tasty lure for fish, their excrement enriches soil and their burrowing loosens it. According to MotherEarthNews.com, earthworm castings are "in short, one of the finest organic fertilizers available." This and other beneficial attributes make small earthworms big business.

References

• Backyard Nature: Earthworms
• MCWDN: Earthworms
• U.S. Department of Energy: Ask a Scientist
• Mother Earth News: How to Raise Earthworms (For Fun and Profit)