How do worms breathe?

Worms have neither a nose nor lungs to breathe through.

Instead worms absorb oxygen through their skin. In order for the oxygen to travel to the worm’s blood stream, the skin must stay moist. The clitellum produces a mucus and air dissolves on the mucus allowing the worms to breathe. If worms dry out, they suffocate.

As fresh air is taken in through the skin, oxygen is drawn into the worm’s circulatory system, and the worm’s hearts pump the oxygenated blood to the head area. The movements of the worm’s body make the blood flow back to the back end of the body, and the hearts pump the blood forward again. Carbon dioxide dissolves out of the blood back to the skin. – Sonya Welter, eHow Editor