Earthworms are smooth-skinned worms, with a body made of many small segments. If you look at the body you can see lines that mark the segments. Each segment has stiff little hairs that help the worm move, sometimes the hairs are hard to see. They have no skeleton, but do have lots of muscles. Earthworms don't have much coloration, so they usually look white, gray, pink, or reddish brown. Some earthworms have red blood, and you can see it through their skin. Their skin produces slimy mucus that helps them slide through the soil. Like most animals they have a front and back end, and their mouth and tiny brain are at the front. They don't have eyes or a nose, but can detect light and vibrations, and have senses of touch and taste. Some earthworm species are very small, less than 1mm long, but some are the biggest worms in the soil. In North America the biggest are almost 30 cm long, and Australia there are some that grow to over 2 meters long!
Earthworms and their aquatic relatives are found all over the world. There are several thousand species! Most live in muck and mud around freshwater, but some live under the sea, and many live in the soil on land. This account is mainly about the earthwoms that live on land. There are at least 21 species of earthworms in Michigan. Some of the biggest and most common species of earthworms in North America were accidentally brought there by colonists from Europe.
Earthworms and their relatives live anywhere there is moist soil and dead plant material. Earthworms are most abundant in rainy forest areas, but can be found in many habitats on land and in freshwater. All earthworm species need moist soil conditions to survive.
Most earthworms species live in the top meter or so of soil, and spend much of their time just below the surface where there is plenty of decomposing plant material. Some species emerge onto the surface at night when it is damp enough. They go deeper to avoid droughts or winter freezes. Some species never come to the surface, and spend their whole lives meters below the surface. Worm tunnels have been found to go at least 5 meters (16.5 ft.) below the surface!
Earthworms lay their eggs in cocoons that they make in the soil. The little worms that hatch out look like tiny versions of the adults, and they don't change much as they grow, they just get bigger. Species that live in very cold or hot and dry climates may go dormant when it is too cold or dry. Some only survive the winter or summer as eggs.
Some earthworm species can live up 8 years, but it is very rare for them to survive that long. Most are eaten or killed in some other way before they live for one year.
During the day earthworms mostly stay in their burrows underground. At night they come up near or on to the surface to feed. If the air it is too cold or too dry, they stay down in the soil. Some species also come on to the surface during the day if it is raining.
Earthworms only communicate with each other by touch and taste, but they can feel vibrations, and often avoid predators by sensing their footsteps. They can also sense light and moisture in the air.
Earthworms eat dead and decaying plant material, mostly leaves, but also tiny roots and other bits. Some species live down deep in the soil and eat dead roots.
Earthworms' main defense is hiding in their burrows in the soil. They will quickly crawl down into the ground if they detect a predator. Some can secrete bad-tasting chemicals. Some can also grow a new tail.
Earthworms are very important to the soil. They carry organic material down into the lower levels, they break down dead plant material, and their burrows help air and water get deeper into the soil.
Earthworms sometimes damage seedlings of valuable plants, and by moving around in the soil may spread plant diseases. Some earthworms also carry animal parasites that grow in their predators.
Earthworms are usually very beneficial. Their tunneling and feeding helps to enrich soil, promoting better plant growth.
Earthworms as a group are very common and abundant, and are not in need of special protection. We don't know very much about most species though, so some rare species could be in danger.
It's not true that if you cut a worm into bits the parts will grow. Sometimes they can grow a new tail, but that's it. The worms that come out during rainstorms are looking for new places to live, and often get trapped in puddles. They can live in water (they get oxygen through their skin), but they will die from too much sunlight, or if there is salt or other toxic chemicals in the puddles.
Some people keep boxes of worms and dirt. They feed the worms kitchen scraps, and then put the worms and dirt in their gardens.