Earthworms live in the soil of every continent in the world except for Antarctica! There are about 2700 different kinds of them.
They aren't much to look at (they may even seem a little gross), but earthworms are really good at what they do. You might be surprised to learn that their job is a very important one. So, what do they do? They dig tunnels through soil in the ground. As they go, they eat, digest their food, and then excrete it. That doesn't sound very important. Well, it turns out, the "waste" that worms excrete is actually very valuable for soil. It is full of nutrients that help plants grow. The tunnels they form also help keep the soil healthy by supplying it with oxygen and making it easier for water to soak into the ground. Worms periodically come up to the surface of the ground to find food, then go back down and continue tunneling. This process helps mix up the richer soil from farther down in the earth with the soil at the top. This is important because lots of the nutrients in topsoil have already been used up by plants and the soil down below has more nutrients. All of these things make the soil better for plants to grow in. This is important for us since most of our food comes from plants or from animals that eat plants.
Earthworms are excellent recyclers! They eat things like fallen leaves and decaying animals. They can also eat food scraps, fruit and vegetable peels, eggshells, and some garbage (like coffee grounds and tea bags). Organic matter - something that came from a living thing, such as a plant or animal - will break down on its own eventually, but an earthworm can eat and digest an amount of food and dirt equal to its own weight in a single day, so the process goes much faster with their help! This keeps the soil full of helpful nutrients.
Worms need food, oxygen, and moisture to live. They breathe through their skin instead of with lungs. Oxygen from water in the ground can pass through a worm's skin to keep it alive. They like the soil to be damp so that their skin can stay moist and slimy, but not too wet. If you go outside after a rainstorm, you might be able to spot some earthworms on the sidewalk. Sometimes after heavy rain, earthworms come up to the surface because they've gotten too much water while in the ground. UV rays from sunlight can kill worms very quickly, though, so if the rain storm happens during the day and the sun starts shining again, earthworms that have come up to the surface often get burned by the sun's rays and die. If you happen to see any earthworms on the sidewalk, it's a good idea to use a stick to move them back to an area with dirt.
Earthworms are very simple creatures. They don't have arms, legs, or ears. Instead of eyes, they have special cells on the outsides of their body that are very sensitive to light. Those cells help them see light, but nothing else. They have small simple brains that are used to help them move their bodies. They can also have up to five hearts to help pump blood through their long bodies.
An earthworm's body is divided into lots of segments and they have a head end and a hind end. The very first of the tiny segments is the earthworm's mouth and the last segment is its anus, where waste, called castings, exits its body. Both ends look similar, but you can tell the head end by the thick ring-like segment that is located near it.
An earthworm's mouth is very small, but it is strong enough that it can hold onto a leaf and drag it around as the worm moves! When an earthworm eats, it uses a muscle in its throat to move the food down into a little space called a crop. The food stays in the crop for a little while, sort of how food stays in your stomach for awhile. Then it is pushed into another space called a gizzard. The gizzard has large grains of sand and small stones in it from the sand and dirt the worm has eaten. To digest the food, the gizzard squeezes in and out and the sand and stones rub together and grind up the food! From there it passes through the worms intestines where the worm gets all the nutrition it needs from the food. Then it exits the worm's body as castings.
Most plants start their life as some sort of seed. A seed has all of the information it needs to grow into a plant, but before it can grow, it needs certain conditions to be right. When it has everything it needs (warmth, oxygen, and water), it will sprout. The sprouted seed will soon grow a stem above the ground. Below the ground, it will grow roots. The roots grow downwards into the soil. Roots are very important for plants. They help hold the plant in place in the soil while it grows. They also provide water and nutrients that the plant can't live without. The roots soak up nutrients and water from soil, then the nutrients move up the roots into the stem of the plant to reach the leaves, flowers, and fruit. Roots have tiny hairs on them to help absorb water and nutrients from the soil. Sometimes plants use their roots to store extra food, especially during the winter.
Do you remember what plants need in order to grow? They need sunlight, air, and water. They also need nutrients. The best way for plants to get nutrients is from soil. As you've already learned, earthworms help provide soil with lots of great nutrients. A plant's roots are the parts that allow a plant to use the nutrients that the worms provide. Roots help plants grow, and then earthworms eat the leftover parts of plants and the cycle starts all over again!
There are several different kinds of roots. Some plants have many roots and some just have a few. Trees have large systems of roots - some really big ones to help hold the tree up safely in the ground, and lots of smaller ones to help the tree get water and nutrients. Some vegetables, like carrots, radishes, and turnips, are actually roots! They are called taproots, because they just have one long main root. Sugar comes from a type of root, called a sugar beet, which is similar to a root vegetable.
Besides keeping a plant in place, roots can help keep soil in place. For example, the roots from trees growing along the edge of a river or near an ocean can help hold the soil in place when water washes over it.