Earthworm

Earthworms stay dirt-free with special skin that attracts water from the soil.

Has it ever struck you as strange that when earthworms crawl out of the ground, they generally look clean and free of dirt? If you crawled around in dirt all day, how do you think you would look? How do earthworms manage to stay clean despite moving through dirt all day?  

You can demonstrate how earthworms stay clean using a balloon and thin stream of water (e.g. from a faucet). Simply rub the balloon against your shirt (this friction is similar to the friction of an earthworm against the soil it is crawling through). Then bring the balloon close to the stream of water. Ask pupils to observe how the water bends towards the balloon.

Simple explanation

When the earthworm crawls, friction between the worm and soil changes the worm’s skin. The worm’s skin, and water in the soil, now act almost like magnets. As the earthworm crawls through the soil, water actually moves towards it. It’s as though the earthworm gets a constant shower as it travels through the soil.

More detailed explanation

It turns out earthworms have special skin, which cleverly uses the resources around it to stay clean. When an earthworm starts to move, the friction against the soil causes its skin to accumulate tiny, microscopic parts of the dirt on it, called electrons (the same thing happens to your hair when you pull your head through a sweatshirt: your hair acquires electrons from the friction against the sweatshirt – electrons are part of everything). But how does this end up cleaning the earthworm?

Soil is like a sponge, and it can hold a lot of water in it, in between the soil particles. Each tiny piece (i.e. molecule) of water has both a positive and a negative side, similar to how a magnet has a north and south pole. As the earthworm moves through the dirt, the positive side of the water in the soil gets attracted to the electrons accumulating on the earthworm’s skin. So, as the earthworm moves through the soil, the water in the dirt actually moves towards the earthworm (similar to how your hair stands up whenever your sweatshirt is near). This build-up of water makes the soil around the earthworm more slippery, and this makes it easier for the earthworm to move through the soil. This build-up of water next to the earthworm as it crawls through the dirt also helps keep the earthworm clean. It’s as though the earthworm gets a constant shower as it travels through the ground.

So, even though it has crawled through dirt all day, when the earthworm emerges on the surface of the Earth, it’s clean and free of soil.

People have learned an idea from earthworms that they hadn’t thought of before. Just like it makes it easier for an earthworm to move when soil isn’t stuck to it, it takes less energy for equipment like tractors and bulldozers to move when they aren’t caked with mud. Could we learn from earthworms how to keep things like tractors clean?

If you pass a small electric current (a flow of electrons) through the metal of a tractor, the water in the mud stuck to it will collect between the tractor and the mud, causing the mud to just slide off. Researchers have demonstrated that we can dramatically improve energy efficiency this way. Equipment that uses less energy requires less fossil fuel or less renewable energy to do work, which can reduce pollution.

Some STEAM opportunities include:

• Everything in the world is made of atoms.
• Molecules are contructed of atoms.
• One part of an atom is an electron, which can have either a positive or negative charge.

Discover how elections wiggle (read more here).