Wow! The Wonders of an Earthworm

How Diffusion Allows an Earthworm to Breathe


    Ah … this earthworm is about to become a tasty snack!

    But even if the bird doesn’t eat the earthworm right away,
    our earthworm friend will probably die if he stays in the sun for
    too long.  Why?

    The secret to staying alive is in his skin …
    and a scientific process called diffusion.


    Look closely at the earthworm’s skin.  Does it look wet to you? Maybe a little bit moist? You might already know that we find earthworms in damp soil, and perhaps you have seen earthworms crawling on the ground right after a  hard rain or a major storm.  Why do
you think this is?  If you answered that an earthworm needs to live in a damp environment – but not too damp – you’re right! To understand the reason why, though, we need to look a little more closely.
Earthworms certainly don’t look like humans – and one difference between earthworms and us is the way that we breathe.  Earthworms need oxygen just like humans, but they don’t have lungs like we do.  They have a special skin that allows them to “breathe” oxygen right through it.  How does this work?  It has to do with a science concept called diffusion.
Diffusion is the movement of molecules from an area of higher concentration (think crowded) to an area of lower concentration (less crowded).  Diffusion allows an earthworm to get the oxygen it needs to survive.  Remember, an earthworm needs oxygen just like we do, and its cells are constantly using oxygen to perform cell processes.  This means the amount of oxygen inside the earthworm will always be less (lower concentration) than the area outside of the earthworm (higher concentration).  This is great news for the earthworm! New oxygen from the environment is constantly diffusing into the cell to replace the oxygen that is used up.
Okay, you get diffusion.  The same process that keeps oxygen coming in to the earthworm also keeps carbon dioxide going out, getting rid of this waste for the earthworm. But we still haven’t answered our question about why the earthworm needs to live in a damp environment.
A moist surface is necessary for oxygen to be absorbed and carbon dioxide to be given off.  The worm’s skin is protected by a thin cuticle and kept moist by a slimy mucus.  This lets it absorb the oxygen it needs and expel carbon dioxide.  If a worm is dried up by the sun, it will die because the exchange of gases can’t take place.
Well, why doesn’t an earthworm just stay underground when it rains, then, instead of coming to the surface? Not a bad idea – it definitely would stay moist!  Scientists aren't really sure of the answer. Some think too much water is a bad thing, because  that water takes the place of valuable air in the soil.  Air contains more oxygen than water does, and remember, earthworms need oxygen.  Without it, the earthworm would suffocate!  Other scientists, though, have different ideas about why earthworms crawl to the surface after it rains.  These researchers say earthworms can survive underwater for a little while, but come to the surface after the rain because it is easier to move on a wet surface.  Can you think of a way to test these ideas? 

Sounds like a good research project! What we do know is that earthworms require a certain balance of water to survive.

And now you know just how important the process of diffusion is for an earthworm – and why an earthworm needs to stay moist in order for diffusion to take place.

                                                                            For a diffusion challenge, please go to:
                                                                            More About Diffusion
                                                                            For more detailed information on this topic, please go to:
     Biology Concept Paper
     For more fun facts about worms, check out
     MISEP student Ryan Lenet's webpage
    Picture credits:
    Bird with Earthworm
    Cartoon Worm