Life's Little Mysteries

Why Does Rain Bring a Flood of Earthworms?

Earthworms come out when it rains

Some rain dances don't occur until showers begin, like the splishy-splashy tip-toe you do around the earthworms on your sidewalk and driveway. Rain causes the worms to leave their drenched burrows and swarm the pavement in order to help regulate their breathing.

It's not that worms don't like to get wet. On the contrary, they need to stay damp in order to breathe properly.

Earthworms don't have lungs. They breathe through their skin. Oxygen dissolves into a mucous coating on a worm's skin then passes through the skin and into blood vessels. The skin must be moist for the oxygen to pass. Special glands secrete the mucous to keep things consistently gooky.

Balance is the key. Too dry is bad: If worms dry, they die. Too wet is bad too: Worms can survive in water for two weeks, but they can't absorb sufficient oxygen from water, and eventually they suffocate.

Why are there so many earthworms on your driveway? Because there can be as many as one million of them under one acre of soil. Step lively!

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