Everyone has met an earthworm at some point in their life. Whether you think they’re neat, or think they’re gross, earthworms are little creatures that play a big role in the ecosystem. Learn why they do what they do (like scatter on sidewalks after it rains) and how they help us.
Biology and Habitat
Think an earthworm is just an earthworm? Think again. There are 23 families, over 700 genera and more than 7,000 species of earthworms. They can grow anywhere from two inches to two yards, depending on the species. Even though there are so many different types of earthworms, all share some basic features. Earthworms are cold-blooded, segmented worms, that are hermaphroditic, meaning each worm has both female and male sexual organs. They mate by joining their clitella, exchanging sperm and then forming their own egg capsule. Baby worms hatch from tiny cocoons.
Earthworms breathe through their skin and will live wherever there’s food, oxygen and humidity. There may be more earthworms living near you than you would think—one acre of land can be home to over one million earthworms.
Behavior and Diet
Earthworms compost and recycle. They dig deep tunnels into the ground, tilling soil in the process. They decompose dead and organic matter and glean their food from any bacteria and fungi growing nearby.
Earthworms do seemingly bizarre things. Have you ever wondered why do earthworms come out in the rain? The simple answer for why worms appear after rain is because this is when above-ground conditions are most favorable. Earthworms stay underground for much of their lives but prefer to mate above-ground. Rain creates humidity and moisture, which worms need, and creates the perfect time to come out of the dirt. Also, they come to the surface to increase their oxygen intake, since worms can’t transfer oxygen easily in the flooded ground.
Ecological Importance
As worms dig through dirt, they mix topsoil with subsoil and secrete a slime full of nitrogen, which is important for plants. Earthworms increase microbial 
activity by cycling nutrients via digestion. Their excrement contains higher levels of microorganisms than the originally-consumed matter. This excrement creates a soil called aggregate soil that’s mixed into deep layers. Earthworms act as one collective garden ho, tilling the soil and mixing in more nutrients.
Scientific Classification
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata