Have you ever seen a sidewalk full of worms after a rain storm? Some people think worms are just gross creatures, but there are thousands of different types of worms. This lesson will examine three main categories of worms and other wiggly worm facts.

What is a Worm?

Have you ever dug through the dirt or played in a rain puddle and discovered a worm? These ground worms are often found in gardens and parks, but they are just one of the many thousand different species of worms. Even though there are many types of worms, nearly all have a few attributes in common. Almost all worms have long, slender bodies without any appendages (legs or arms). Worms, regardless of species, are all invertebrates, or creatures without a backbone. This helps give worms that wiggly, squishy reputation.

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Now it could be hard to keep track of all the worm species, but thankfully most worms can be placed into three categories: flatworms, roundworms, and segmented worms. Let’s explore these three types of common worms.


Flatworms are just that: flat. In fact, they kind of look like tennis shoe laces or small plastic bags. Flatworms have one hole used for eating and discarding waste. If a flatworm is sliced in half, it will turn into two flatworms. Not all worms have this cool ability!

There are over 20,000 types of flatworms. Some are parasites. Parasites live inside or on another animal. They get their nutrients from the animals they reside in. A commonly known parasitic flatworm is the tapeworm. Tapeworms are often found in the intestines of cats, dogs, and people. Flatworms that are not parasites live in oceans and lakes around the world.

A Tapeworm


Roundworms are cylindrical like a spaghetti noodle. They can be microscopic (so small they can only be seen with a microscope) or a little over 12 inches long. That’s longer than the length of a normal piece of writing paper. Unlike flatworms, roundworms have a head and a tail end to their bodies. These worms also lay eggs instead of splitting into multiple worms.

When you think of worms you may think of them slithering along like a snake, but roundworms can’t move that easily. They can only move by bending their thin bodies into ‘C’ and ‘S’ shapes. This makes these worms look like angry jumping beans under a microscope. They need moist or wet areas in order to move more freely. Like tapeworms, roundworms are often parasites that live in animals and humans.

A Roundworm

Segmented Worms

If you take a walk on a cold, wet morning you may see worms wiggling around on the ground. These are most likely earthworms and fit into the segmented worm category. Segmented worms have connected sections or segments to their bodies. A segmented worm is kind of like a slinky or a group of connected rings.

The common segmented earthworm is a big help to the environment. They live in soil, eat decomposing materials, and create tunnels that aerate the ground for the roots of plants. These worms have little bristles called setae on their bodies that help them dig through the dirt easily. Most earthworms are only a few inches long, but keep your eyes out for the few that grow to 14 inches. That’s probably longer than the keyboard you are using right now!

An Earthworm

Lesson Summary

Worms are invertebrates and may have long, skinny bodies. There are several different types of worm species, but most worms can be put into one of three categories: flatworms, roundworms, and segmented worms. Many worms are parasites and live in or on other animals.