The tiny creatures darting around your pool are almost always one of a handful of common aquatic insects or larvae, with water boatmen, backswimmers, and mosquito larvae topping the list. Most are harmless nuisances drawn to your pool by the same things that make it appealing to you: standing water, warmth, and light. Figuring out which bug you’re dealing with determines whether you have a minor annoyance or something worth addressing quickly.
Water Boatmen
Water boatmen (family Corixidae) are the most common swimming insect you’ll find in a residential pool. They’re oval-shaped, about 6 to 12 millimeters long, and brownish or greenish. Their hind legs are flattened and fringed with tiny hairs, which they use like oars to paddle through the water in short, jerky bursts. If the bugs you’re seeing swim near the bottom or along the walls and don’t seem bothered by your presence, they’re likely water boatmen.
These insects don’t bite. They feed primarily on algae and tiny organic particles, which is actually a clue about your pool’s condition. If water boatmen have shown up, there’s a good chance your pool has a thin film of algae growing somewhere, even if you can’t see it with the naked eye. The algae is their food source, and without it, they have little reason to stick around. Addressing the algae problem, which we’ll get to below, is the most effective way to send them packing.
Backswimmers
Backswimmers (family Notonectidae) look similar to water boatmen at first glance but behave very differently. The giveaway is in the name: they swim upside down, belly-up, just beneath the water’s surface. They’re roughly the same size as water boatmen but tend to be lighter in color on their underside, which faces the sky as they swim. Their body shape is more keeled, like a tiny boat hull.
Unlike water boatmen, backswimmers are predators. They eat other small insects, including mosquito larvae and water boatmen themselves. And here’s the part that matters for you: backswimmers can and do bite. The bite feels like a bee sting, sharp and surprisingly painful for such a small creature. It’s not medically dangerous for most people, but it’s unpleasant enough that you’ll want to deal with backswimmers promptly. They tend to show up in pools that already have a population of smaller insects to feed on, so their presence usually means there’s an existing bug problem attracting them.
Mosquito Larvae
If the “bugs” in your pool look more like tiny wriggling worms than swimming insects, you’re probably looking at mosquito larvae. They hang just below the surface, breathing through a small tube at their tail end, and they move by jerking their bodies in a distinctive s-shaped wiggle. They’re sometimes called “wrigglers” for exactly this reason.
Mosquito larvae are a red flag. Female mosquitoes lay eggs in any standing water they can find, and a poorly maintained pool is a prime target. Research on freshwater colonization has found that mosquito larvae are among the most pollution-tolerant aquatic insects, thriving in nutrient-rich or degraded water where other aquatic species cannot survive.1Journal of Arid Environments. The impacts of an invasive herbivore (Camelus dromedaries) on arid zone freshwater pools: An experimental investigation of the effects of dung on macroinvertebrate colonisation In pool terms, that means stagnant, under-chlorinated, or neglected water is an open invitation. A well-maintained pool with proper circulation and chlorine levels won’t support mosquito larvae for long, because the chemicals kill them before they can develop into adults.
Speed matters here. Mosquito eggs can hatch within 24 to 48 hours in warm water, and the larvae can become flying, biting adults in as little as a week. If you see wrigglers, act the same day.
Less Common Visitors
A few other creatures show up in pools often enough to be worth knowing about:
- Springtails: These are extremely small (around 1 mm), wingless, and tend to cluster on the water’s surface rather than swimming beneath it. They look like tiny dark specks that jump when disturbed. Springtails feed on organic matter and mold and are completely harmless. They usually appear after rain or when vegetation is close to the pool edge.
- Thrips: Another very small insect, slender and barely visible. Thrips don’t actually live in water; they blow into pools from nearby plants and gardens. You’ll notice them floating on the surface. They can give a mild nip if they land on your skin, though it rarely amounts to more than a brief itch.
- Water beetles: Several species of small diving beetles find their way into pools. They’re typically round or oval, dark-colored, and fast swimmers. Most are predatory, eating smaller insects and larvae. Some can bite if handled but generally avoid contact with people.
- Midges and gnats: These are not the same as mosquitoes, though they look similar. Midge larvae are often tiny, translucent, and threadlike. Adult midges don’t bite, and the larvae are harmless. They’re more common in pools near lakes, ponds, or marshes.
Dragonfly and damselfly larvae occasionally turn up in neglected pools as well. These are larger, predatory, and actually helpful in that they eat mosquito larvae. But they’re unusual in chlorinated water and mostly show up in pools that have been sitting unused for weeks.
Why Bugs Are Attracted to Your Pool in the First Place
Insects end up in pools for two main reasons: the water itself and what’s living in it. The water attraction is surprisingly well understood. Many aquatic insects locate bodies of water by detecting horizontally polarized light, the specific type of light reflection that a flat water surface produces. Research on this behavior has found that it operates through mechanisms distinct from sky-based navigation, suggesting these insects have a dedicated sensory response that draws them toward any surface with the right kind of reflective properties.2PubMed Central. Insect Responses to Linearly Polarized Reflections: Orphan Behaviors Without Neural Circuits Your pool’s smooth, glassy surface is essentially broadcasting “water here” to every insect in the area that relies on this kind of detection.
That explains why bugs arrive. What determines whether they stay is food. Algae is the foundational food source in the pool-bug food chain. Microscopic algae grows when chlorine levels dip, when phosphates accumulate, or when the filtration system isn’t running enough. Water boatmen eat the algae. Backswimmers eat the water boatmen. Mosquitoes breed in the standing water. Each layer of the problem feeds the next, which is why a pool with one type of bug usually develops more over time if the underlying conditions aren’t corrected.
Pool lights are another draw, particularly at night. Many flying insects navigate by light sources, and a lit pool on a dark evening will pull in everything from beetles to moths. The insects that can’t swim drown on the surface; the ones that can swim, like water boatmen and backswimmers, dive in and stay.
Getting Rid of Pool Bugs
The good news is that the solution for nearly every type of pool bug is the same set of basic maintenance steps, because the bugs are all responding to the same underlying conditions.
Start with your chlorine. Free chlorine should stay between 1 and 3 parts per million for a standard residential pool. If it has dropped below that range, algae starts growing, and the whole cascade begins. Shocking the pool, temporarily raising the chlorine level to around 10 ppm or higher, kills algae, mosquito larvae, and most other organic matter in the water. After shocking, run the pump and filter continuously for at least 24 hours to circulate the treated water and filter out dead material.
Brush the pool walls and floor before or during the shock treatment. Algae clings to surfaces, and the chlorine works better when you’ve physically disrupted the film. Pay attention to spots with poor circulation: corners, behind ladders, around steps, and anywhere the water tends to be still.
Check your phosphate levels. Phosphates are essentially fertilizer for algae, and they enter pools through rainwater runoff, lawn chemicals, skin products, and decaying leaves. Your local pool supply store can test for phosphates and sell you a phosphate remover if the levels are high. Historically, researchers have found that combining algicidal agents with even low concentrations of chlorine produces a much stronger effect against algae than either treatment alone.3PubMed Central. Algicidal and sanitizing properties of Armazide This principle still holds: a good algaecide paired with proper chlorination does more than doubling down on chlorine alone.
For the bugs themselves, a manual skim with a fine-mesh net is the fastest immediate fix. Water boatmen and backswimmers can be scooped out by hand (or by net, if you’d rather not get close to backswimmers). Mosquito larvae die quickly once chlorine levels are restored, but skimming them out removes them even faster.
Preventing Bugs from Coming Back
Consistent pool chemistry is the single biggest factor. A pool with properly maintained chlorine and pH simply doesn’t support the algae that starts the whole food chain. Test your water at least twice a week during swimming season, and adjust as needed. If you’re using a salt chlorine generator, make sure it’s producing enough chlorine; these systems can fall behind during heat waves when chlorine demand rises sharply.
Run your filter pump long enough. In warm weather, the pump should run at least 8 to 12 hours a day. Stagnant water is a breeding ground; moving water is not. Mosquitoes in particular avoid laying eggs in water that has any surface disturbance.
A few physical barriers help too. Pool covers, when the pool isn’t in use, block insects from reaching the water. Reducing vegetation immediately around the pool removes habitat for springtails, thrips, and other insects that would otherwise be close enough to wander in. Trimming overhanging trees and shrubs also cuts down on the organic debris that feeds algae.
If your pool lights are bringing in insects at night, consider switching to LED lights with a warmer color temperature or turning off underwater lights when no one is swimming. Some pool owners install bug zappers or yellow “bug light” bulbs in nearby fixtures to draw flying insects away from the water.
Are Pool Bugs Dangerous
For the vast majority of pool owners, the answer is no. Water boatmen are harmless. Backswimmers deliver a painful but medically insignificant bite. Springtails, thrips, midges, and water beetles pose no real threat. The one exception that genuinely matters is mosquitoes, not because the larvae themselves are dangerous, but because adult mosquitoes transmit diseases. If your pool is breeding mosquitoes, you’re potentially contributing to the local mosquito population, which is a public health concern beyond just your backyard.
There’s an occasional question about whether water bugs in general can transmit diseases. In tropical regions of West Africa, certain aquatic insects in the Corixidae and related families have been found to harbor the bacterium that causes Buruli ulcer, a skin disease. Research from endemic areas detected the pathogen’s DNA in roughly one in ten pooled insect samples collected from natural water sources, with one subfamily showing rates as high as about 44 percent.4PLOS Neglected Tropical Diseases. Seasonal and Regional Dynamics of M. ulcerans Transmission in Environmental Context: Deciphering the Role of Water Bugs as Hosts and Vectors This is specific to certain tropical environments and to natural freshwater habitats, not chlorinated swimming pools. It’s not something a pool owner in North America, Europe, or Australia needs to worry about in a maintained pool. But it does illustrate that aquatic insects can carry pathogens in the right conditions, which is one more reason not to let your pool become a stagnant, untreated body of water.
When a Pool Sits Unused
The scenario where pool bugs become a serious problem isn’t the well-used backyard pool that occasionally gets a water boatman. It’s the pool that goes neglected. Vacation homes, foreclosed properties, and pools that are drained partway and then collect rainwater are some of the worst offenders. A pool that hasn’t been treated in weeks can become an entire functioning ecosystem: algae coating the walls, water boatmen feeding on the algae, backswimmers feeding on the water boatmen, mosquitoes breeding in the still water, and frogs or toads showing up to eat the insects.
If you’re reopening a pool that has been sitting, don’t just shock it and hope for the best. Skim out as much debris and as many visible organisms as you can first. Test the water thoroughly, because pH and alkalinity may have drifted far outside normal ranges, and adding chlorine to extremely unbalanced water is less effective. You may need multiple rounds of shocking, brushing, and filtering over several days to fully clear a green, bug-infested pool. In severe cases, partially draining and refilling with fresh water is faster and cheaper than trying to treat water that’s gone fully swampy.
If you’re closing a pool for the season, a solid winter cover that seals tightly against the deck keeps insects and debris out for months. Mesh safety covers allow rainwater through, which means they can still collect standing water on top, and that small puddle on the cover is enough for mosquitoes to breed in. Pumping water off the cover regularly avoids that problem.
Bugs That Look Like They’re Swimming but Aren’t
Not every creature you see moving in your pool is actually an insect. A few common look-alikes cause confusion:
- Copepods: These are tiny crustaceans, not insects. They’re barely visible to the naked eye and move in quick, jerky hops through the water. Copepods are completely harmless and typically show up in pools with organic buildup. Proper chlorination eliminates them.
- Worms: Thin red or brown worms occasionally appear, especially after heavy rain. These are usually bloodworms (midge larvae) or earthworms that washed in from surrounding soil. Bloodworms are the larval stage of non-biting midges. They’re not parasitic and pose no health risk.
- Tadpoles: If frogs have been visiting your pool, you may find tadpoles. They’re easy to distinguish from insects by their size and shape but can alarm pool owners who aren’t expecting them. Scoop them out and relocate them to a natural body of water if you can; chlorine is lethal to amphibians.
White or translucent flecks drifting around near the surface are often not living creatures at all. They may be pollen, calcium scale flakes, or biofilm fragments. If the specks don’t move on their own when the pump is off, they’re debris, not bugs. A good skimming and a filter cleaning usually takes care of it.