Dr. Universe explains why worms come out when it rains

By Communications staff, Washington State University
Cartoon illustration of Dr. Universe, a smiling gray cat wearing a white lab coat and crimson WSU shirt, holding a red umbrella as raindrops fall against a cloudy blue sky.
WSU’s Dr. Universe explores why earthworms come to the surface when it rains and how wet weather helps them survive and move around.

Washington State University’s resident feline scientist, Dr. Universe, answers a question from Courtney of Idaho: Why do worms come out when it rains?

With help from WSU soil scientist Tarah Sullivan, Dr. Universe explores why earthworms sometimes leave their underground homes during rainy weather.

Readers learn that earthworms don’t have lungs. Instead, they breathe through their moist skin, absorbing oxygen and releasing carbon dioxide. When heavy rain fills the air pockets in soil with water, worms may head to the surface in search of better breathing conditions.

But avoiding waterlogged soil isn’t the only possible explanation. Rainy days also provide cool, damp conditions that allow worms to travel aboveground without drying out, making it easier for them to find new places to live.

The column also highlights the important role earthworms play in keeping soil healthy by breaking down organic matter and recycling nutrients.

Ask Dr. Universe is a science education project from WSU that answers real questions from curious kids around the world. Readers and listeners can submit their own questions and explore more columns, videos, and the Ask Dr. Universe podcast online.

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