Why Do Worms Surface When It Rains?

Updated: Jul 9

Have you ever walked outside after it rains and noticed the sidewalks and pavement are covered in worms?

(Photo via Shutterstock)

Scientists don't fully understand why worms do this, but they have a few ideas. One theory is that coming above ground when it rains helps worms move more quickly than they can while burrowing tunnels underground. Above-ground travel is only possible when it's raining or right after because they need moisture and cannot travel across dry ground.


The vibrations created by raindrops may also draw worms to the surface when it rains. Worms may think the vibrations are from predators like moles moving through the soil. Worms will move toward the surface to escape a mole. They may do the same thing when it rains because they think the vibrations are from predators.


For many years, scientists thought worms surfaced during a rainstorm so they wouldn’t drown when water filled their burrows. However, we now know this isn't true. Worms won't drown when it rains. They actually need moisture in the soil to breathe, because they breathe through their skin. Worms can even survive underwater for days.


No matter why they come to the surface in the rain, we frequently see evidence that they don't always make it back underground fast enough after it stops. You can help a worm or two after it rains by moving them off the pavement or sidewalk and onto the nearest patch of dirt or grass. This will allow them to more quickly burrow back underground.


We benefit from having earthworms hard at work under our feet. They are not essential for healthy soil, but having them in the dirt is a good sign that the soil is healthy.


All their digging and crawling through dirt has many benefits. Worms improve the soil's ability to hold water and increase its filtration. They create channels to allow plant roots to grow, and they mix soil and stimulate microbial activity, which helps plants get nutrients from the soil.


And while you may think a worm is a worm is a worm, there are a lot of different kind of worms. Earthworms are divided into 23 families, and there are more than 7,000 different species! Most of the worms we see aren’t native to the United States. They came here from Europe when settlers arrived.


Although most worms aren't harmful to the ecosystem, a few worms are considered invasive. One example is the jumping worm. These worms are harmful to the ecosystem because they change the soil in a way that makes it harder for native plants to grow.

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