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Why do Worms Come Out When it Rains?

After it rains, the conditions above ground are moist which makes it easier for worms to breathe and move across the ground.
Earthworms.
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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 30 October 2014
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Many people have noticed that after a rain, worms appear in gardens, on sidewalks, and scattered across neighborhood lawns, much to the delight of local birds. Modern humans are far from the first to make this observation: authors dating back to the Renaissance have noted the appearance of worms after a rain. There are several interconnecting factors to explain why they come out when it rains, but the short story is that worms find conditions above ground to be especially favorable then.

A common myth about worms is that they are forced to come out of their holes during the rain because they would drown if they stayed below. In fact, this is not true. Worms breathe through gas exchange, absorbing oxygen directly through their skins. As long as water has sufficient dissolved oxygen, worms can actually live for several days fully immersed in water, as scientists have discovered.

The way in which worms breathe does explain why they tend to congregate above ground after the rain, however. Worms are covered in a mucus that facilitates gas exchange, and as a result, they must stay moist. Most of the time, conditions above ground are too dry and hot for worms, and they will dry out and die because they cannot breathe. After a rain, the environment is moist, facilitating breathing and also making it easier to crawl along the ground, so worms are encouraged to surface.

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As for why worms come out above ground at all, worms prefer to mate above ground. They often come out after a rain in the hopes of finding mates, treating the above-ground world like a sort of worm discotheque, with a wide sampling of potential mates available. Studious observers may have noted that worms often congregate in small groups above ground, illustrating their primary reason for surfacing. Worms, incidentally, are simultaneous hermaphrodites, so both partners exchange sperm, which is used to fertilize eggs.

In addition to surfacing after a rain, worms come out at night as well. During the evening hours, the air is typically much cooler, and the environment is often moist, making it hospitable to worms. People who use worms for fishing bait often choose the evening hours to go hunting for “nightcrawlers,” taking advantage of this trait to collect worms for fishing trips.

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anon333705
Post 14

This worm mystery really interests me. I was expecting to see worms anytime there was rain in a 24 hour period, but not always so. In Utah, in April 2013, I picked up about 500 worms along our neighbor streets. I tried repeating on other days when we got the same amount (.11 inch rain) or more (.43" & .5") but no worms. It was 41F on April 11. This morning the rain gauge recorded .11", but no worms to rescue. I have 1.5 acres, and put the rescued worms in my garden, away from areas with concrete/blacktop.

anon312803
Post 13

There has been a heavy rain for two days now and my sidewalk is covered with worms, some lifeless and some still crawling. It appeared that they were trying to enter my garage. I figured they needed the dryness so I filled a bucket with potting soil and picked every "live" one up.

When it finally stops raining, I will place them back in yard or my compost bin. Was this the wrong thing to do? Did I keep them from finding their mate? Should I put them back on the sidewalk in the rain?

anon251296
Post 12

I have never seen worms coming our of my lawn for years when I don't have a professional gardener. Now, the worms are all over when it rains.

In the backyard, there are no worms after a professional gardener working there. Is the weed killer forcing the worms to come out during rain?

anon179782
Post 9

Also, we can help worms too! We can help them by picking them up after it rains and then putting them some where is the grass, or in the dirt! Cool! And i never knew that frogs came out when it rains. Do they really?

Wait, also i told my family that and that they guessed wrong! They guessed that they come up from the ground because it gets to wet in the moist earth ground when it rains. Is that cool or what? Man, i really love this article. It really made me think differently about worms! And now they are my pals! I love worms!

And guess what? I also learned about them on this TV show called "Wild Kratts". Its a nice TV show. And it helped me a lot too! Thank you for changing my way of thinking about worms!

anon159632
Post 7

Okay if they come out to mate when it's wet, why don't they go back to the dirt when it starts to dry? Instead they dry up on the sidewalk and die and make the most annoying mess to clean up! Ever tried cleaning up dried stuck to the concrete worms? Not a fun job unless you have a power washer!

would like to know how to stop them from coming out onto the sidewalks? Can you put a substance down around the edge of your grass to stop them from crawling on the concrete sidewalks or driveways?

anon153256
Post 5

Can't let my dog go out after rain or he is in wormy wormy hunting heaven. good article very informative.

anon110599
Post 4

Last Friday, our Church lawn was covered with hundreds of earthworms! they looked like hundreds of shiny twigs scattered across the garden. The weather was mild and the grass was damp. Could the music coming from the church have attracted them?

anon87031
Post 3

I have never seen frogs come out after it rains -- only worms!

anon37851
Post 1

why do frogs come out in the rain

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