A worm is a small, soft-bodied animal with no legs that lives in soil, water, or sometimes inside other creatures. Earthworms are the most familiar kind: they tunnel through dirt, eating decaying leaves and helping make soil rich and healthy for plants. If you've ever dug in a garden after rain, you've probably seen these helpful creatures wriggling around.

Worms have played a quiet but vital role in agriculture for thousands of years. Charles Darwin, the famous naturalist, spent years studying earthworms and concluded they were among nature's most important workers, constantly turning and enriching the soil. Without worms, gardens and farms would struggle to grow healthy crops.

The word worm also describes anything that moves by twisting and squirming. When you worm your way through a crowd, you're squeezing between people like a worm moving through soil. Someone might worm information out of you by asking subtle questions until you reveal a secret. And if you “open a can of worms,” you've started dealing with a problem that turns out to be more complicated than you expected, with one issue leading to another and another.