by chelsea schuyler

Why Do Earthworms Come Out in the Rain?

Behold the earthworm. I would like today to focus on this serpentine slime beast and point out some oddly unknown, awesome facts.

You mean, besides having FIVE hearts and yet never featuring on Valentine’s Day cards? besides being the only ones who know exactly what it’s like in a wormhole yet are never asked? besides grossing people out instead of getting respect for their role in the general health of basically All Land Everywhere? Yes.

A friend asked me “When it rains and the sidewalk is besieged by worms, are they trying to escape drowning in mud or are they happy for the opportunity to go swimming across the sidewalk?” As usual, I had never considered this. So I dun looked it up.

Hypothesis 1: Avoiding Drowning

Indeed, the common thought was that earthworms came up because they are trying to avoid drowning. Turns out this is a common mammalian, lung-centric assumption. Earthworms breathe through their skin, getting oxygen through diffusion, a process requiring moisture, so it’s actually being too dry that will make them suffocate. They can live submerged in water for days, even weeks. (Which I’m sure was discovered in a totally PETA approved experiment.)

Yet, didn’t we know this already? Fisherfolks, back me up here, if we can throw a worm into a river for hours and expect them to squirm for fish, whilst being speared with a metal hook no less, wouldn’t they be okay with a little moisture in their tubes?

Anyway, whatever, the point is we don’t think it’s a drowning thing anymore. Nor do we think they’re using the chance to mate cuz only a few species mate above ground (you wanna do it, up there? in front of god and everyone? Have some decency woman!).

(Remember that joke about the indecent feminine worm? Good times. But I should point out that earthworms are hermaphroditic, having both the girl parts and the guy parts, so leave your slut shaming comments to a min. kthanxbai)

Hypothesis 2: Exploration

My friend’s latter hypothesis (that worms just want to swim on sidewalks) turns out to be a pretty astute speculation. Our guess now is that rain time is a worm’s best chance to get around without a bunch of pesky dirt to chew through or sunshine to incinerate in.

This is the superhighway of wormland, their continuing mission, to explore uncramped worlds and nontunneled civilizations–space being, indeed, the final frontier. Unfortunately, a lot of that space has been paved by cement-happy humans, which I think is the only sidewalk connection.

But then again, I don’t get that we have the real motivation here, cuz it’s not like they never come out otherwise. They feed on plant litter at night, hence the early bird getting the worm, it’s still dark enough that the worms are out. And hence the alternate name, “nightcrawler.” So why all the craze when it rains? Wouldn’t they rather sleep in? A couple ideas:

Hypothesis 3, 4, 5, 6:

• Sure they can survive for days in water, but maybe it’s totally uncomfortable being in suspended animation for that long.
• Though worms are without eyes, there is still a sensor in their heads that can sense light so they won’t go vaporize themselves during the day. Maybe when it rains, the cloud cover makes it dark enough that they know a party on the surface is gonna rock.
• Over-oxygenation. Ironically, scientists think that perhaps the worms are sensitive to the rush of oxygenated water. An ironic opposite of drowning.
• Maybe they just got places to be. A guy’s gotta go to the grocery once in awhile you know?

Non-Hypothesis: Moles

One theory we can rule out, scientists assure us, is moles.

And thank god for that.

Did You Know: that if you shove a stick into the ground, then rake a flat piece of metal over the protruding end, over and over, the earthworms will sprint out of their holes like rats to a pied piper? It’s called worm-grunting, and there are festivals and competitions for it in Florida that got so out of hand they had to regulate it with permits to make sure they didn’t kill off all the worms in the state.

Ah, Florida.

Anyway, it works because the vibration mimics the sound of a worm’s top enemy, the mole. How fisherman accidentally discovered this trick without knowledge of the mole factor is a mystery, but at least we can clear the proposed practice round to Whack-a-Mole, “Whisper-a-Worm,” for fact-checked accuracy.

Rain Experiment: Fail

Once scientists verified that worms erupt like fireworks in the presence of a mole, they wondered, ‘What if raindrops also sound like mole vibrations, and confuse the worms into emerging?’

But when they created rain onto worm-bins with 300 worms, only 6 emerged. After 24 hours of the soil being completely saturated with standing water on the surface, they examined the worms and all appeared to be healthy. Not afraid of drowning, and not thinking that rain was a mole. To which worms responded, “yeah, shocking. Screw you guys.” To which humans responded, “dude, you thought a stick was a mole.” To which worms responded, “suck it, it’s uncanny!”

But Wait, Worms are Awesome Experiment: Success

Speaking of mysterious motivations, the really interesting thing that scientists discovered is that worms make group decisions. Belgian PhD student Lara Zirbes, et al aimed to study how worms interact with microorganisms, but noticed meanwhile, that the worms often moved together after touching.

So naturally they put a bunch of worms into a central chamber that had two arms extending out in different directions. After squirming all over each other, the worms almost always went together to one side of the chamber over the other. It’s the first documented, collective orientation of any animal influenced by touch.

“We can consider the earthworm behavior as the equivalent of a herd or swarm.”

Whoa, let’s go with herd. ‘Swarm’ may not have the best, non-panic inducing connotations, and earthworms have enough PR problems as it is.

The next question they want to pursue is the why. Individuals of these Belgian worms secrete fluids that contain antibacterial properties and a yellow goo that puts off the predatory flatworm. Safety in mucousy numbers? Or maybe it’s just lonely being blind, deaf, and stuck in a dark hole all the time. I don’t know, too lung-centric?

Worm MythBuster

One final buzzkill before I go – if you cut a worm in half it doesn’t turn into two worms. The part with the head might live through it and grow back, but the butt end, that’s just gone. That myth was kind of a dead end. It won’t ever grow to its full potential. But its got a good head on its shoulders.