Understanding the Origin of Earthworms in Post-Rain Pool Environments
Marcus Thorne
A Familiar Post-Rain Mystery
If you own a pool, you have probably walked out after a gentle overnight shower or a big thunderstorm and found a surprising scene: clear blue water dotted with earthworms. Sometimes it is just a handful near the skimmer. Other times it looks like half the lawn decided to go for a swim.
From a pool automation and maintenance point of view, this is more than an “ick” factor. Worms add organic load to the water, clog baskets and filters, and throw off your hard-earned water balance. At the same time, the very presence of those worms is usually a sign that your soil and landscaping are alive and working the way nature intended.
To manage the problem without losing your sanity or harming your backyard ecosystem, it helps to understand what earthworms are actually doing when it rains, how they end up in your pool, and which prevention strategies are worth your time and money.
In this article, I will walk through the science behind worm behavior after rain, connect that science to what we see in real backyard pools, and then translate it into practical, low-drama solutions you can pair with your automation and cleaning routines.
What Earthworms Are Really Doing When It Rains
Many of us grew up with the simple story that worms come up during rain so they do not drown. It sounds logical, but modern research paints a more nuanced picture.
How Earthworms Breathe and Move
Earthworms are soil-dwelling invertebrates that breathe through their skin rather than lungs. For gas exchange to work, that skin has to stay moist. Dry soil can literally suffocate them because their skin dries out and oxygen can no longer diffuse in, a point emphasized by pest-control explainers such as Fenix Pest Control.
On the flip side, soaking wet conditions do not automatically mean doom for worms. Articles from The Nature Conservancy’s Cool Green Science blog and Scientific American note that many species can survive fully submerged in water for days, even up to a couple of weeks, as long as there is enough dissolved oxygen. So flooding alone does not force every worm to the surface.
Movement is part of the story too. Instead of legs, worms move by rhythmically contracting and expanding their bodies while tiny bristles on each segment grip the surrounding soil. In loose, moist soil this is efficient. In dry, compacted dirt it is slow, exhausting work because the gaps between soil particles shrink and tunnels become harder to form, as described by Fenix Pest Control’s overview of worm locomotion.
When rain softens the ground, it opens those gaps and lubricates the soil, making it much easier for worms to burrow. Just as important for our pool story, a rain-soaked surface gives them a rare chance to travel above ground without drying out.
Why Worms Come to the Surface
Scientists and naturalists, including writers for Cool Green Science, the Earthworm Society of Britain, and Scientific American, highlight several overlapping reasons worms emerge during and after rain.
First, wet surfaces act like high-speed highways. Tunneling underground is slow compared with sliding along a moist lawn or path. A storm gives worms a short window to disperse farther to find food, mates, or new territory without the risk of desiccation. Many soil ecologists see this “migration opportunity” as one of the most convincing explanations.
Second, oxygen conditions change in saturated soils. Studies summarized by Cool Green Science and other science writers describe species-specific responses: some worms with higher oxygen demand struggle when their burrows are waterlogged and less oxygen is available. Those species are much more likely to surface during rain, while others with lower oxygen demand stay put underground. So oxygen stress in soggy soil can push certain worms upward, but it is not a universal rule.
Third, vibrations play a role. Worms are very sensitive to vibrations in the soil. Traditional practices like “worm grunting” or “worm charming” deliberately create vibrations that mimic predators such as moles and reliably drive worms to the surface. Raindrops hitting the ground can create similar vibrations. The Earthworm Society of Britain and various science writers note that vibrations from rain may be one of the cues worms use to move toward the surface, although lab tests have not fully nailed down how strong this effect is compared with moisture and oxygen.
What this means for your backyard is simple: after rain, worms are not staging a mass suicide. They are using the storm as a chance to move, breathe, and survive, even if a small percentage of them get it wrong and end up on pavement, sidewalks, or, unfortunately, in your pool.
From Soil to Skimmer: How Worms Actually Reach Your Pool
Once worms are above ground, there are several specific pathways that bring them from your soil into your pool. These paths differ slightly between in-ground and above-ground designs, but the underlying pattern is consistent across pool-owner reports, service blogs, and even online forums.
In-Ground Pools: Runoff, Coping, and Hidden Openings
In-ground pools are usually surrounded by some mix of coping stones, pavers, concrete decks, and landscaping. Earthworms naturally live in the nearby garden beds, lawns, and mulched areas where the soil stays moist and rich in organic matter. Pool-maintenance articles from Pool Spa and Filtration Supplies, RMD Pool Service, and other service companies all describe a similar chain of events.
During heavy or prolonged rain, soil near the pool becomes saturated. Worms surface to escape low-oxygen pockets and to take advantage of the wet conditions for faster migration. As they crawl across the softened ground, they often approach the edges of coping, concrete, or paver decks.
From there, two things typically happen.
First, worms simply cross the hardscape and slip in. The coping and deck are wet, and in many yards they slope gently toward the pool. That slick surface combined with gravity makes it easy for worms to slide over the edge into the water, especially where the coping sits just a little above the surrounding soil.
Second, worms are carried by runoff. When rain flows off roofs, decks, and paths and toward the pool, it can wash worms along gutters, drainage lines, expansion joints, and cracks in concrete. RMD Pool Service notes that worms can even be guided into the water through small cracks in the surrounding decking or landscaping that channel runoff straight toward the pool basin. Owners in online groups echo this, reporting that after big storms they find worms concentrated near places where water visibly drains into or across the pool.
There is also one less obvious pathway. In some concrete or gunite pools, worms can come up through the hydrostatic relief valve at the floor of the deep end. That valve is designed to let groundwater into the pool shell if pressure under the pool gets too high, protecting the structure. A comment shared in a concrete pool owners’ group describes worms surfacing through that valve, especially noticeable at spring opening. There is not much a homeowner can do to stop that particular route without risking structural issues, so it is best treated as an occasional maintenance nuisance rather than a solvable design flaw.
Above-Ground Pools: Crawling Up and Slipping In
At first glance, an above-ground pool seems well protected. There is a vertical wall, often metal or resin, and a smooth vinyl liner on the inside. Yet many owners still report finding worms in their above-ground pools after rain.
A discussion summarized from a Straight Dope message board helps explain why. Worms are actually quite capable climbers as long as they have traction. The tiny bristles that help them move in soil also give them grip on rough or damp surfaces, including the outer wall of an above-ground pool.
They can crawl up the outside and over the top rim. The problem starts once they cross that rim. The top rails are usually smoother, and the inner surface of the pool wall and liner is smoother still. On that slick, curved surface, especially when wet, their bristles cannot get a good grip. It only takes the smallest misstep for a worm to slip off the edge and drop into the water.
Once inside, they are essentially stuck. Water removes the friction they rely on, and the vertical, slick vinyl wall offers almost nothing to hold onto. Unlike insects that can swim or kick hard enough to reach the side and climb out, worms simply wriggle in place and eventually tire out.
The key takeaway from the above-ground perspective is that worms do not intentionally “jump” into the pool. They are following their usual instinct to move across damp surfaces and explore, but the smooth design of the pool rim and walls turns a normal crawl into an accidental fall.
Why Worms Cannot Get Back Out
Whether you have an in-ground or above-ground pool, once worms end up in the water, their odds of escape are poor.
Several sources note that worms are fine in moist environments where gravity presses them against a surface and their bristles can dig in. In open water, gravity does not help them in the same way. Their bodies are neutrally buoyant enough that they float or drift rather than staying firmly pinned to a wall or floor. On a smooth vinyl or fiberglass surface with circulating water, they cannot generate enough friction to pull themselves upward.
Inside the vessel, things are even harder. Skimmer weirs draw surface water across a narrow opening; once a worm reaches that opening it is pulled into the skimmer basket. Those baskets are excellent at catching worms but terrible at letting them self-rescue. In many homeowner accounts and service blogs, dead worms end up decomposing there, creating slimy clumps and bad odors until someone empties the basket.
So even though lots of worm species can survive in water for days under the right conditions, a swimming pool is not the right environment. Smooth surfaces and circulation turn survivable immersion into a one-way trip.
Are Earthworms in Your Pool Dangerous?
From a health perspective, the typical backyard earthworms you find in your landscaping are not a major threat to swimmers. Articles aimed at pool owners, such as those from PoolPartsToGo and RMD Pool Service, consistently frame worms as a nuisance and maintenance issue rather than a direct health hazard.
Worms themselves do not release toxins into the water, and standard pool sanitizers are very effective at controlling the everyday microbes that might hitch a ride on soil and organic debris. One service blog even reminds owners to keep chlorine levels within recommended ranges year-round partly because proper disinfection also controls microscopic parasitic worms, which are quite different from the visible earthworms that aerate your soil.
The real downsides are indirect:
Worm bodies, plus the bits of soil and leaves they bring in, add organic load to the water. If you leave them to decay in the pool or filter system, they can cloud the water, feed algae, clog filters, and make it harder to keep chemistry balanced. Worm build-up in skimmer baskets is notorious for causing foul odors if it is not cleaned out, as noted by pool professionals in service blogs.
From a risk management standpoint, the best approach is simple. Treat worms in the pool as you would any other organic debris. Remove them promptly, keep your sanitizer and circulation in the recommended ranges, and you will keep your swimmers safe and your water clear.
Backyard Heroes, Pool Nuisances: The Ecology Angle
It is easy to dislike worms when you are fishing them out of your skimmer on a humid morning. But zoom out just a little, and those same worms are doing important work in the soil around your pool.
Ecologists describe earthworms as “ecosystem engineers.” Reviews of soil biodiversity and climate impacts on earthworms note that in many temperate soils, worms make up a large share of the animal biomass underground. They burrow, mix soil layers, create channels that improve water infiltration, and break down organic matter into nutrient-rich castings. Garden-oriented sources highlight that worm castings are rich in nitrogen, phosphorus, and potassium and that worm activity helps build dark, fertile humus.
Several gardening and ecology articles emphasize that high earthworm activity around your yard is often a sign of healthy, living soil. Their presence supports better plant growth, more stable soil structure, and improved drainage. Even discussions of climate change and earthworm communities highlight that worms can moderate runoff and erosion by enhancing soil structure, though extreme shifts in moisture and temperature can stress some species.
In other words, if you have enough worms around your pool to notice them in the water after rain, that usually means the surrounding soil is in good shape, not that something is wrong.
The trick is to keep their benefits in the garden and lawn while minimizing their accidental visits to your pool.
Here is a simple way to look at it.
Location |
Role of earthworms |
What it means for your pool |
Garden and lawn |
Aerate soil, improve drainage, recycle nutrients, support plant health |
Healthier landscaping, stronger root systems, better runoff control overall |
Pool deck edge |
Crossing zone between soil and hardscape during wet weather |
Higher chance of worms reaching coping and slipping into the pool |
Inside the pool |
Dead organic debris and soil particles |
Extra cleaning work, more filter maintenance, chemistry swings if ignored |
The goal for a stress-free backyard is not to eliminate worms altogether but to interrupt the routes that lead them from the “good” column into the “extra work” column.
Practical Ways to Reduce Worms in Your Pool After Rain
You cannot stop the rain and you probably do not want to get rid of worms in your yard. But you can make it much harder for them to end up in your pool, and you can make cleanup almost automatic by pairing physical strategies with smart automation.
Clean Up Promptly After Storms
Every article aimed at pool owners agrees on one basic point: after rainy periods, a little extra attention pays off fast.
As soon as it is safe to do so, skim worms and other debris from the surface and empty skimmer baskets. Vacuum the floor to remove any soil that made it in with the worms. Doing this promptly keeps decay and odor from getting ahead of your sanitizer and filtration.
If you have a pool automation system, this is a perfect place to let it work for you. Many owners set a “storm follow-up” routine that runs the pump longer or triggers a robotic cleaner cycle the morning after heavy rain. Even if you still have to net a few worms by hand, automation can dramatically cut down the labor and help your water recover quickly.
Shape the Landscape and Deck to Direct Worms Away
Several service articles, including those from RMD Pool Service, Pool Spa and Filtration Supplies, and Blue Science, point out that worms are most abundant where you have rich, moist soil, thick mulch, and lush plantings. Those are great for your garden, but they are risky when they sit right against your coping.
Moving the worm “hot spots” slightly away from the water can make a big difference. Some pros suggest keeping soil beds and dense plantings at least about 20 feet from the pool edge when possible. Even a smaller buffer of hardscape between the water and the richest soil will reduce the number of worms that ever reach the deck.
Adjusting drainage is just as important. If your deck slopes toward the pool, or if gutters and downspouts send rain straight across the coping, you are effectively building a worm conveyor belt. Where feasible, regrade small sections of deck, redirect downspouts, or add drains so that runoff flows away from the water instead of toward it. Hardscaping choices such as pavers, gravel borders, or concrete bands at the waterline can further separate soil from pool.
The pros of this approach are that it also helps with general cleanliness, reduces soil wash-in, and improves safety on wet decks. The downside is that some changes, like moving established landscaping or re-pouring deck sections, can be time-consuming or expensive on an existing pool. Many owners tackle these gradually during other renovation projects.
Adjust Soils Near the Pool Without Overusing Chemicals
One creative approach highlighted in a PoolPartsToGo article is to use a narrow band of crushed limestone in the soil bordering the pool. Raising the soil pH in that strip makes conditions less appealing to worms, encouraging them to stay farther back in the yard.
This method has clear pros and cons. On the positive side, it is a non-insecticidal way to discourage worms in a very targeted area. On the caution side, you must apply it carefully. Heavy rain can wash limestone dust into the pool and push your water pH upward, and dramatically altering soil pH over a wide area can affect the broader soil ecosystem.
Across multiple sources, there is strong agreement that broad-spectrum insecticides are a bad choice here. They may kill some worms, but they also harm beneficial insects like bees, ladybugs, spiders, and butterflies that help your garden and pollinate your yard. For worm control around pools, physical and habitat-based strategies are strongly preferred.
Use Covers and Automation to Your Advantage
Covers are one of the most effective ways to keep rain-driven debris out of the water, and worms are no exception. Pool Spa and Filtration Supplies, PoolPartsToGo, and various owner forums all point out that putting a cover or floating blanket on the pool before a storm drastically cuts the number of worms that make it into the water.
Solar covers and automatic covers do double duty. Besides blocking debris, they also reduce evaporation and heat loss. One pool equipment article notes that pairing a solar cover with an efficient heat pump can significantly shorten the time it takes to warm a pool. For example, a 95,000 BTU heat pump can raise an 18,000 gallon pool from around 66°F to 82°F in roughly two days under favorable conditions, and high-efficiency variable-speed pumps can cut energy costs by a large margin compared with older single-speed units.
From an automation perspective, covers are where your “backyard tech” side can really shine. Many systems let you:
Create routines that remind you to close the cover when rain is in the forecast.
Integrate with weather alerts so a “storm mode” closes the cover and adjusts pump schedules automatically.
Pair cover status with pump and heater logic so you save energy and keep chemistry more stable.
The main downside is that covers add cost and a bit of operational friction if you are not using automation. But if worms and other debris are constant headaches, a well-used cover is one of the most effective long-term fixes.
Work with, Not Against, Your Hydrostatic Valve
If you have a gunite or concrete pool with a hydrostatic relief valve in the deep end, you may occasionally see worms appear from that point, especially when you open the pool in spring. As one pool owner put it, there is little you can do to stop worms entering through that safety device.
The reason is structural. The valve is there to relieve groundwater pressure that might otherwise lift or crack the shell. Blocking it or altering it to keep worms out risks serious damage. The practical, low-stress approach is acceptance and routine cleanup: when you open the pool, expect some worm accumulation at the bottom and plan to vacuum it out as part of your standard start-up. Once that initial clean is done, many owners report very few worm problems for the rest of the season.
Above-Ground Pool Tweaks
For above-ground pools, the key vulnerabilities are the climbable exterior and the slippery interior. While you cannot make the inner wall rough enough for worms to climb without also making it harder to clean, you can make the outer path less inviting.
Some owners and pool writers suggest:
Reducing direct soil contact with the outer wall by adding gravel or hard edging.
Using simple edging, small borders, or slightly raised pads around the base so worms have to climb modest inclines before reaching the wall, something they are not great at.
Paying attention to where rainwater flows from nearby beds and directing that away from the wall so worms are less likely to be carried right up to the pool.
The reward here is that these changes often help with other issues too, such as weed control and splashback mud. The trade-off is that they can take a weekend of digging and some new materials, so many owners phase them in as part of broader yard improvements.
Short FAQ: Common Worm-and-Pool Questions
Do earthworms in my pool mean the water is unsafe?
In most backyard situations, no. The visible earthworms that aerate your soil are primarily a cleanliness issue, not a direct health threat. They bring in organic debris that can cloud water and feed algae, but standard sanitizer levels, circulation, and prompt cleanup are sufficient to maintain safe swimming conditions.
Should I spray insecticide around the pool to stop worms?
That is not recommended by the pool and garden sources summarized here. Insecticides may harm a wide range of beneficial insects and other wildlife and do little to address the real pathways worms use to reach the pool. Physical barriers, drainage improvements, landscaping adjustments, covers, and good maintenance give you better results without collateral damage.
Why do I sometimes see many worms one year and hardly any the next?
Worm activity at the surface depends heavily on moisture patterns and temperature. Reviews of earthworm ecology and climate effects note that worms are most active when soils are moist but not bone dry or permanently waterlogged, and when temperatures are moderate rather than extremely hot or cold. Years with frequent, soaking rains and mild weather tend to bring more worms to the surface and, by extension, more accidental worm visitors to pools. Drier years or those with more extreme heat or cold may produce fewer visible worms, even if the underlying populations are still there.
Closing Thoughts: Working With Nature, Not Against It
Earthworms in your pool after rain are a classic example of how healthy backyard ecology and low-maintenance pool ownership can bump into each other. The same creatures that quietly aerate your soil and feed your plants can become slimy debris in your skimmer if your deck, drainage, and habits give them a path to the water.
By understanding why worms surface in wet weather and how they physically end up in both in-ground and above-ground pools, you can choose smarter, calmer responses. A bit of landscape tweaking, thoughtful use of covers and automation, and a consistent post-storm cleanup routine will keep your water clear without waging war on the living soil that makes your backyard feel alive.
The goal is not a sterile, worm-free yard. It is a clean, easy-to-care-for pool nestled in a thriving landscape, where your tech, your maintenance habits, and nature are all pulling in the same direction.
References
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6944501/
- https://www.reconnectwithnature.org/news-events/the-buzz/nature-curiosity-why-do-worms-come-above-ground/
- https://blog.nature.org/2019/04/15/the-real-reason-you-see-earthworms-after-rain/
- https://www.researchgate.net/publication/337592719_Climate_change_effects_on_earthworms_-_a_review
- https://www.earthwormsoc.org.uk/FAQrain
- https://www.poolspa.co.za/help-ive-got-earthworms-in-my-swimming-pool/
- https://smart.dhgate.com/why-do-worms-come-out-when-it-rains-exploring-the-reasons/
- https://fenixpestcontrol.com/why-do-worms-come-out-when-it-rains/
- https://www.iancollmceachern.com/single-post/the-science-behind-worms-appearing-after-rain
- https://poolpartstogo.com/blogs/articles/how-to-get-rid-of-worms-in-your-pool-and-keep-them-out?srsltid=AfmBOooEHbqhvgUKIVQEF2_wc4hz3Y-0-yNoVyXUGvgn-KSGODTHoL_r
