Why Do Earthworms Come Out When it Rains?

I’ve always wondered why earthworms come out of the ground when it rains.  I don’t know about you but after a rain I can always find them on driveways and roads.  Sometimes I’ll see thousands of them on a short stretch of road as if they are having some kind of mass annelid exodus from a field on one side of the road to the other.  So what gives?

Earthworm on Pavement After Rain

Earthworm in my driveway

At times I’ve wondered if a hard surface like concrete or asphalt provides a source of relative warmth over wet soil.  As it turns out the answer is pretty simple.  They can’t breath underground when the soil is saturated.  The air pockets in the soil fill up with water and worms basically breath through their skin.  Teri Balser is an associate professor of soil and ecosystem ecology at UW-Madison and she says, “Oxygen from air or water passes directly from their outer cuticle into their blood vessels. Normally, soil has a mix of air and water — about 50 percent of the pore space in soil is air, the rest is water. Oxygen diffuses easily through air, and the soil stays aerobic because oxygen comes in from the surface.”

So that’s all there is to it, and now I know better.  Rather than suffocate the worms move elsewhere.  I’d probably do the same thing.  Hopefully I won’t lay in the middle of a road and get squished though.


Earthworm in cover crop

An big, fat earthworm crawling through our cereal rye cover crop

Another article claims they may reveal themselves in such great numbers following a rain for a number of other reasons.  Stemming from the possibility that “they can even survive several days fully submerged in water” some experts believe pounding rain may mimic the vibrations of worm eating predators causing the worms to surface.  Another thought is they may be using the wet conditions to travel longer distances overland than they could underground.  Since the surface is wet they don’t have to worry about drying out in the hot sun.


What’s your worm experience?  Why do you think the come out on a rainy day?

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    1. I would love to know if there is anything I can do to prevent worms from surfacing, I have lived in my house for 22yrs and seen earthworms infrequently after rains until this year. Now after it rains there are thousands and thousand all over my driveway in particular congregating all around my garage. They ball up in groups of several hundred. Its gross they smell and eventually die creating a stencth. They are crawling up my garage doors and wedging themselves in cracks. Every rain produces thousands. I thought after the first time it would lesses but it has increased. I saw a thread of someone else that had this issue back in 07 but the advice he got was useless. If anyone has anything intelligent to comment Id love to hear it.

      1. Hire someone who needs a quick easy way to make money (pre-teen) & pay them a nickel for every worm the collect into a home depot bucket or by weight bc u may not wanna count to confirm their count

        Weight the bucket empty and pay a penny for an Oz. Or figure something like that out so they don’t die and cause smells or have time to get into ur garage. Hire him or call around to friends with kids etc the day it’s raining and eventually they’ll know they r coming to ur house the day after the rain
        And you will have less worms to deal with. Before u know it Ull have kids from blocks away wanting to get buckets and head to ur house with rain boots on!

        Good luck. I just collected a few fast food cups worth bc we r going fishing this weekend. So after those kids get those worms u could give them to local fisherman or sell them to replace the money u paid the kids. Or let the kids have fun selling them at a worm stand (like lemonade stand) at a near by fishing area.

      2. hi I jst started seeing the worms this year after the snow I been in my house 5 yrs in july never ever seen this before I found 3 in my living room all stretched out also in my drive way and patio I put sulfar down to keep them off the porch

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