Why do earthworms come out after rain?

Asks Amy Robinson

We breathe oxygen from the air with our lungs. An earthworm breathes oxygen by absorbing it through its moist skin. It likes damp soil, but if the rain is very heavy, the oxygen in the water-logged soil may run out. Then the worm has to come up into the air to breathe. On top of the wet ground, the worm can breathe and wriggle along. It might find a new home, or even a mate. But the worm is only safe above ground in the dark. When daylight comes, the worm is in trouble. A bird may eat it and the sun’s heat and ultraviolet light will kill it.

Photo by Wikimedia Commons