eli5: Why do worms get out on the asphalt when it’s raining?


eli5: Why do worms get out on the asphalt when it’s raining?

In: 3592

First off: gonna lead with a lesser known fact: worms can’t drown. They breathe through their skin and can handle water as easily as air. Their problem with bodies of water is that they can’t *move* because there’s nothing for them to push off of and against.

Edit: because others are asking: okay, they *can* drown in the sense that they can’t live in the water indefinitely because water has less easily available oxygen then air. They’re not aquatic. They can, however, still breathe somewhat and live in the water for a few weeks.

For the question: Worms have a slime coating on them that helps them move without every little bump in the ground tearing their skin. Worms don’t come up during the day because it’s not safe from birds and such that would eat them and also because the sun can dry them out. (They do sometimes come to the surface at night because the sun isn’t there to kill them, and also to escape burrowing animals like moles.) But they often come up in the rain because it’s suddenly as easy for them to move and survive on the surface as it is underground without the danger of drying out. They try to cross the asphalt because they’re able to and also to find new dirt. They’re everywhere, they’re just more noticeable on the asphalt because they’re stuck there when the water is gone.

Edit: I didn’t come here to be known as the worm guy but apparently this blew up? This one comment is already a not-insignificant portion of my karma, what is happening?!

Edit edit: I don’t know about snails or slugs, stop asking me.


Worms can sense the change in atmospheric pressure which indicates coming rain. While it’s true that they absorb oxygen through their skin, they move out of the ground preemptively to avoid drowning as water holds less oxygen than air. Even when the soil isn’t rained upon, such as in a covered, plastic worm compost bin, the worms will come out and climb up the sides and out of the bin.



Haha, I get looks all the time outside of where I work.. I end up having to save dozens on my walk to my vehicle.

If you put a tuning fork or a pitchfork into the ground make it vibrate they will come up I always assumed worms came up when it rained because of the rain hitting the ground making a (vibrational) resonance frequency that made them try to escape the ground!

I have the same question but for snails, in my college campus theyre everywhere when it rains

There’s a good Wild Kratts episode where they talk about it. Something with being easier to move and the sun won’t bake them unless they get caught out once it becomes sunny and dries out.

I have a follow-up question!

I’ve lived in Ontario and in BC. In ON, when it gets ‘wormy’ out, it smells wormy. I can tell they’re out even before I see them. In BC, it does not smell wormy. If its dark, I could be stepping on them and I wouldn’t know! Yes, I have a phobia. But why does it smell in ON and not in BC???

One theory is that when it’s rainy it’s prime time for a worm to find a mate. Worms can only move on wet surfaces and it is easier for them to find a mate while on the surface because they move faster compared to being underground and they are more likely to bump into each other. This is supported by the fact that only some of the worm population will surface during the rain and the vast majority of them are adults.

So the worm on the asphalt in the rain could just be a horny worm looking for mate.



I am always trying to save the worms and put them back in the dirt because they end up all dried on the sidewalk. When we had a pool I’d have to dish so many worms out of the pool on rainy days trying to save them.

Related question: is it just me or are there fewer worms out on the street than when you were little?