Form & Function of Earthworms

Earthworms are more than just squiggly things.

Earthworms are tubular creatures with a digestive system and two main blood vessels extending the length of their bodies. Unlike most creatures, earthworms have no eyes, noses or mouths. Earthworms have evolved in this fashion because they spend their lives underground burrowing through soil and thus have no need for sight. Although they are sightless, earthworms are equipped with light sensitive cells in their skin. An earthworm makes up for its lack of eyes, mouth, complex brain and lungs by sporting five hearts.

Survival

Earthworms thrive in moist, rich soil. When confronted with extremely dry or hot conditions, they burrow more deeply underground and sometimes ball up, cover themselves with mucous, and go into a hibernating state. They are able to slow down their body functions and wait for conditions to become more beneficial.

Movement

Earthworms don't have feet, legs or skeletons. They are able to move because they have a complex system of muscles and tiny protrusions on the outside of their bodies. When a worm wants to move, it stretches itself out, sticks the front protrusions into the ground, and pulls the rest of itself forward. Then it anchors the rear protrusions and pushes its front part forward again. These protrusions are also useful for anchoring itself in its hole when a predator is trying to extricate it.

Benefits

Earthworms are important for soil health. They collectively consume and excrete vast amounts of soil, increasing its nutrient level and usefulness to plants. They also create burrows through the soil that help to distribute nutrients. Additionally, earthworms nourish the soil with their bodies when they die.

Reproduction

Earthworms are hermaphroditic, meaning they possess both male and female organs. They reproduce through a complex process involving two worms exchanging sperm, which later fertilize the eggs. After fertilization, the eggs are jettisoned by the worm into a small cocoon that is left in the soil, from which the baby worms emerge.

Threats

Earthworms are threatened by pesticides. They also succumb to paved surfaces, which they crawl onto when the pavement is wet during rains. When the pavement dries, they dry up and die. Earthworms are prey to and an important food source for many types of animals, particularly birds.

References

• Nature Watch: Worm Watch
• Backyard Nature: Earthworms
• Thames Valley District School Board: The Earthworm