There’s nothing quite like rain on a quiet summer afternoon. Bright blue skies giveaway to a gloomy yet gentle gray. The clouds cascade and brood in chaotic harmony with the deep rolling rumble of thunder. The smell of petrichor permeates through all else as the storm makes itself known to each of your senses. From beneath the surface, the quiet soil beneath your feet, the worms wigg—hey, hold up, what’s up with that anyway? Why do worms come out when it rains?
Well, it depends on who you ask. Unfortunately, we can’t ask the worms directly, but it turns out that plenty of scientists have been asking this very question for, well, a very long time. Today, we explore the leading hypotheses for what drives worms to the surface for these rainy-day adventures.
Seeking a bAlance of Moisture and Oxygen
Worms and soil go together like peanut butter and jelly. What might not be so obvious is that worms need to breathe—something they’re surprisingly able to do just fine in the dark dirt beneath our feet. This isn’t to say that worms emerge because they’d otherwise drown in their subterranean burrows as is commonly believed. See, worms don’t have lungs like you and I. Instead, they breathe by absorbing oxygen through tiny pores in their skin. In fact, they actually need a delicate balance of moisture and oxygen to make that happen. When it rains, the normal balance of the soil is disrupted, as are the conditions on the surface which become more inviting.
It’s sort of like on movies where the astronauts check the readings on some new planet and realize they can take of their helmets. Trouble is, once the sun comes back out and things begin to dry, worms don’t have much time to get back beneath the surface. If they happened to have made their way to something impenetrable for their soft wormy bodies, like a concrete sidewalk or asphalt, it’s pretty much game over.
It’s important to note that different worm species respond differently, depending on their oxygen needs. Those who thrive in little oxygen may remain in the soil, whereas those with higher needs are more likely to emerge.
Picture this: You’re walking barefoot on a pavement, and a sudden rain shower drenches the ground. What do you do? You may seek shelter or step carefully to avoid slipping. For worms, the rain-soaked surface becomes a playground! As the rain saturates the soil, the surface becomes more pliable and easier for worms to maneuver. The lubrication provided by the water reduces friction, making it less strenuous for them to travel across the ground. It may be that rainfall provides optimal conditions for worms to travel to new and faraway places on a grand adventure, like, across the street.
Reproduction and Migration
Rainy weather is an ideal time for worms to engage in reproductive activities. Earthworms are hermaphrodites, meaning they possess both male and female reproductive organs. During the rain, worms seize the opportunity to seek out a mate. It’s possible that they come to the surface to find partners and get their wiggles out. Once their reproductive mission is complete, they may also use the rainwater as a means of dispersal, moving to new areas with fresh resources and opportunities like I mentioned previously.
While worms may not be the fastest creatures, they possess an astonishing ability to sense environmental changes which serves then well when escaping predators. The vibrations caused by raindrops hitting the ground might falsely alert them to the presence of potential predators, like moles. Sensing danger, worms swiftly make their way to the surface, where they are more exposed but less likely to fall prey to their underground adversaries. It’s a clever survival tactic that enables them to evade harm and live to wiggle another day! While certainly a plausible explanation, it’s worth noting that this has yet to be clearly demonstrated in laboratory tests.
Not All Worms
A curious note to consider: not all worms engage in these rainy day side-quests. If they did, you’d certainly see a lot more. In some places, a rainfall would mean the very ground itself would appear to transform into a writhing bowl of spaghetti. Young worms don’t appear to emerge, some species almost never emerge, and the “why” isn’t entirely known. Perhaps determining that “why” is the key in answering the overall “why” behind their rainy day forays.
The next time you find yourself marveling (or gagging, I suppose) at the sight of worms popping up after a summer rain, remember that there’s more to their behavior than meets the eye. Their affinity for rain is not merely a coincidence but a remarkable adaptation that ensures their survival and helps them thrive, though the reasons aren’t 100% certain and are likely a mixture of things. So, the next time you witness these earthy enchanters emerge after a refreshing shower, take a moment to appreciate the intricate dance of nature at play. After all, even the tiniest creatures have their own tales to tell.