ELi5: Why do so many worms appear on roads, sidewalks, driveways, etc. after it rains?


ELi5: Why do so many worms appear on roads, sidewalks, driveways, etc. after it rains?

In: Earth Science

Worms breathe through their skin (they don’t need much, however little filters between the dirt particles is sufficient.. But if the water is saturated with water they can’t, so they dig up to the surface to expose their skin to the air.

All insects need air to breathe, even if they have no lungs. When it rains the water will soak into the ground displacing the air. So in order to prevent drowning the worms have to dig upwards and up to the surface where there is air to breathe. And while moving around on the surface looking for high ground some of them end up on the relatively dry roads.

They’re trying not to drown. Worms instinctually avoid too much water in the soil. Water usually sinks through the ground, so worm’s instincts drive them to dig upwards. If its currently raining the top layers are soaked, so they continue upwards until they run out of ground. Then their instinct is to crawl in search of drier dirt, which they can’t find if the ground is soaked. So they just keep on going.

Because the ground becomes saturated with water and worms like to breathe with air.

Basically, they don’t want to drown.

Longer answer:

They breathe through their skin. Their skin needs to be wet for this to occur. The actually can still breathe when submerged. However, oxygen concentrations in water are not the same as in air and different worms use oxygen faster than others. So some need to surface and get air exposure to increase their oxygen intake.

At first I thought this said women instead of worms and I was trying to remember a time I was stuck on a sidewalk in the rain.

Recently, there’s been more evidence to suggest that worms don’t come out to prevent drowning. They need moisture to breathe and can survive submerged in water for a couple days.

A couple other theories would be that above ground travel is faster than burrowing through soil, and this is only possible when it rains because they need moisture, cannot travel on dry ground, and do not want to burn from the sun. Another theory is due to the vibrations from rain landing on soil being similar to vibrations caused by predators moving through the soil. They may try to reach the surface to escape the predator.

A couple of links: