Several types of aquatic insects can swim in residential pools, but the two most common are water boatmen and backswimmers. Both are strong, active swimmers that are drawn to pools by light, algae, and the water itself. Getting rid of them involves a combination of removing what attracts them, maintaining proper water chemistry, and physically clearing the ones already there.
Water Boatmen
Water boatmen (family Corixidae) are the most frequent uninvited swimmers in backyard pools. They are oval-shaped, usually brownish or dark green, and roughly half an inch long. You will see them darting along the bottom or clinging to the walls, and they tend to show up in groups rather than alone. They are strong fliers as well as swimmers, which is how they find your pool in the first place: they fly from ponds, ditches, or other water sources, spot the reflective surface, and dive in.
Water boatmen feed primarily on algae and microscopic plant material. They do not bite people, which makes them more of a nuisance than a hazard. But their presence is a signal. If water boatmen have taken up residence, your pool likely has at least a thin layer of algae growing somewhere, whether on the walls, the floor, or around fittings. The algae may not even be visible yet, but these insects can detect it before you can.
Backswimmers
Backswimmers (family Notonectidae) look superficially similar to water boatmen but behave very differently. The easiest way to tell them apart is right in the name: backswimmers float and swim upside down, belly facing the sky, using their long hind legs like oars. They are usually lighter in color on the top (which is actually their underside when flipped) and tend to hang near the water’s surface.
Unlike water boatmen, backswimmers are predators. They hunt other insects, including water boatmen, small larvae, and anything else they can overpower. Their mouthparts are adapted to pierce prey and inject saliva that begins breaking down tissue. These insects belong to the order Heteroptera, a group whose predaceous members produce venoms capable of inducing rapid paralysis and tissue liquefaction in their prey, and some species can cause painful reactions when they bite vertebrates as well.1PubMed Central. Venoms of Heteropteran Insects: A Treasure Trove of Diverse Pharmacological Toolkits A backswimmer bite feels something like a bee sting. It is not dangerous for most people, but it hurts, and the welt can last a day or two.
This predator-prey relationship matters for pool management. Backswimmers often show up because water boatmen are already there. The water boatmen arrived because algae was present. So a backswimmer problem is usually a sign that the pool has been slightly off-balance for a while, long enough for a small food chain to establish itself.
Other Insects That End Up in Pools
Water boatmen and backswimmers account for most complaints, but they are not the only bugs you might encounter.
- Water beetles: Several species of diving beetles (family Dytiscidae) and whirligig beetles (family Gyrinidae) can end up in pools. Diving beetles are capable underwater hunters that trap a bubble of air beneath their wing covers to breathe while submerged. Whirligigs are the ones you see spinning in rapid circles on the surface. Both are strong fliers and may land in pools when attracted by lights at night.
- Water striders: These long-legged insects walk on the surface film rather than swimming beneath it. They are common on natural ponds but occasionally land on pools. They are harmless and tend to leave on their own if the water has nothing for them to eat.
- Springtails: Tiny, almost flea-sized arthropods that sometimes appear floating on pool surfaces in large numbers. They are not truly aquatic but congregate near moisture. They cannot bite or sting and are mostly a cosmetic problem.
- Thrips and midges: These tiny flying insects sometimes end up in pools in large numbers, especially during warm evenings. They are not swimmers, just casualties of proximity to water and light. A skimmer net handles them easily.
Mosquito Larvae in Pool Water
Mosquitoes deserve their own discussion because they do not just visit your pool as adults. Females lay their eggs directly on standing water, and the larvae (the tiny wriggling commas you might see near the surface) develop entirely in water before emerging as flying adults. A properly maintained, chlorinated, and filtered pool is generally inhospitable to mosquito larvae. But a neglected pool, a pool that has been sitting uncirculated for a few weeks, or a pool cover with standing puddles on top can become a productive mosquito breeding site remarkably fast.
The larvae of Culex pipiens, the common house mosquito found across much of North America and Europe, are among the most frequent species to exploit neglected pools.2International Journal of Tropical Insect Science. Chronic effects induced by zinc oxide nanoparticles against larvae of the northern house mosquito Culex pipiens (Diptera: Culicidae) A single female can lay a raft of over a hundred eggs, and in warm weather, those eggs can go from hatching to adult mosquitoes in under two weeks. If your pool has been sitting idle, even a short lapse in maintenance can produce a swarm.
The fix for mosquito larvae is straightforward: restore circulation and chlorination. Running the pump moves water enough to disrupt the surface film that larvae need to breathe, and proper chlorine levels kill larvae outright. If you are dealing with a pool that has been out of service for an extended period, shocking it with a heavy dose of chlorine and running the filter continuously for 24 to 48 hours will clear out larvae along with the algae and bacteria that have accumulated.
Why Your Pool Attracts Bugs
Understanding what draws aquatic insects to your pool makes prevention much more practical. Three things pull them in.
Algae is the foundation of the food web. Even a faint green tinge or a slightly slimy feel on the pool walls signals to water boatmen that food is available. Once water boatmen arrive, backswimmers follow because their prey is now conveniently gathered in one place. Eliminating algae is the single most effective step you can take. Without it, water boatmen have no reason to stay, and without water boatmen, backswimmers have no reason to arrive.
Light is the next major factor. Many aquatic insects are strong nocturnal fliers, and they navigate partly by light. A brightly lit pool at night is visible from a considerable distance and acts as a beacon. Outdoor lights positioned near or over the pool surface make the problem worse. If you have a bug problem, dimming pool lights at night or switching to amber-toned bulbs (which are less attractive to most insects) can reduce the influx.
Still water with low or no chlorine is the third attractor. A pool that sits without its pump running develops the same conditions as a natural pond. Insects that evolved to find and colonize small water bodies are remarkably good at detecting these conditions from the air. Circulation and chemical treatment are what separate your pool from a wetland in the eyes of a water boatman.
How to Get Rid of Pool Bugs
The removal strategy works in layers, and tackling them in order matters. Jumping straight to skimming bugs off the surface without addressing what brought them will just leave you repeating the task every few days.
Fix the Water Chemistry First
Test your chlorine and pH levels. Free chlorine should be in the range of one to three parts per million for regular maintenance. If you have visible algae or a significant bug population, shocking the pool (raising free chlorine to around ten parts per million or higher for several hours) is the fastest way to kill algae and make the water inhospitable. Make sure pH is between 7.2 and 7.6, because chlorine becomes significantly less effective as pH drifts upward.
If your pool uses stabilized chlorine products (dichlor or trichlor tablets), be aware that the stabilizer they contain, cyanuric acid, builds up over time. Cyanuric acid acts as a buffer that protects free chlorine from being broken down by ultraviolet light, which is useful up to a point.3PubMed Central. Study on the health risk of cyanuric acid in swimming pool water and its prevention and control measures But when cyanuric acid levels climb too high, it over-stabilizes the chlorine, effectively locking it up so it cannot do its job. The result is a pool that tests positive for chlorine on a strip but still grows algae and fails to repel insects. If your cyanuric acid is above roughly 70 to 80 parts per million, the most practical fix is to partially drain and refill the pool to dilute it.
Brush and Vacuum
After shocking, brush the walls and floor of the pool thoroughly. Algae clings to surfaces, and chlorine alone may not reach colonies that have established themselves in grout lines, behind ladders, or in hard-to-reach corners. Brushing disrupts these colonies and exposes them to the treated water. Follow up by vacuuming dead algae and any debris to waste rather than through the filter, since heavy loads can clog filter media.
Skim and Remove Bugs Manually
Once the water chemistry is corrected, the remaining bugs have lost their food source and will begin to leave. In the meantime, a fine-mesh skimmer net is the most effective tool for physically removing them. Backswimmers in particular will head for the surface to breathe, making them easy targets. Water boatmen that are still alive will try to fly away once their food supply is gone, but any that are sluggish or disoriented from the chlorine shock can be netted out.
Reduce Light Attraction
Turn off underwater pool lights and any bright outdoor lights near the water during the evening hours when you are not using the pool. If you want ambient lighting for the yard, position fixtures so they face away from the water’s surface. Solar-powered or amber-tinted pathway lights are far less attractive to flying insects than white or blue-spectrum LEDs pointed at the pool.
Cover the Pool
A tight-fitting pool cover is one of the simplest long-term deterrents. When the water surface is physically blocked, flying insects cannot land on it, lay eggs in it, or detect the algae beneath it. This is especially valuable if your pool goes unused for stretches during the week. Just make sure no standing water collects on top of the cover, since that puddle can become a mosquito breeding site of its own.
Will Dish Soap Kill Pool Bugs
A widely shared home remedy suggests adding a few squirts of liquid dish soap to the pool to kill backswimmers and water boatmen. The idea is that soap breaks the surface tension of the water, making it harder for insects to float, breathe, and escape. This does work on a basic physical level: many aquatic insects rely on the air-water interface to trap air bubbles against their bodies, and disrupting surface tension can drown them.
The problem is that soap also disrupts your pool chemistry. Surfactants cause persistent foaming, can interfere with filter operation, and interact unpredictably with sanitizers. A small amount in a large pool may seem harmless, but it is difficult to remove once added, and repeated applications compound the issue. A better approach is to use the algae-removal and chlorine-shock strategy already described. It addresses the root cause rather than just killing bugs that are already present, and it does not introduce chemicals that your filtration system was not designed to handle.
Do Pool Bugs Bite, and Should You Worry
Water boatmen do not bite. They are herbivores with mouthparts built for scraping algae, and they have no interest in human skin. Backswimmers, on the other hand, can and do bite if handled or if they bump into a swimmer and feel threatened. The bite pierces the skin and delivers a small amount of venom designed to subdue insect prey. For humans, this typically means a sharp, stinging sensation followed by localized redness and swelling. The pain usually peaks within a few minutes and fades over the next day.
Serious reactions are rare. Most backswimmer bites are comparable to a wasp sting in intensity and resolve without treatment. Washing the area with soap and water, applying a cold compress, and using an over-the-counter antihistamine or hydrocortisone cream if the itching is bothersome is usually all that is needed. If you notice signs of infection at the bite site (increasing redness, warmth, or pus), see a doctor, but this is uncommon.
Diving beetles can also pinch or bite defensively, though encounters are far less frequent than with backswimmers. The sensation is similar, a brief sharp nip, and reactions are generally mild.
Preventing Bugs From Coming Back
Consistent maintenance is the real long-term answer. Bugs exploit the gaps between cleanings, and most pool infestations start during periods when the pump was off for a few days, the chlorine ran low, or a filter issue went unnoticed.
Running your pump for at least eight to twelve hours a day during warm months keeps the water circulating and the sanitizer distributed. Test chlorine and pH at least twice a week during peak swimming season. Brush the walls and waterline weekly to prevent algae from getting a foothold. Keep landscaping trimmed back from the pool’s edge, since overhanging plants drop organic matter into the water that feeds algae and provides cover for insects. Empty or treat any standing water nearby, including birdbaths, planter saucers, and forgotten buckets, to reduce the overall insect population in your yard.
If you use an automatic chlorinator, check it regularly to make sure it has not run out of tablets or malfunctioned. A chlorinator that quietly stops working can leave your pool unprotected for days before you notice the water starting to turn. By that point, algae has already begun growing, and the food chain that ends with backswimmers darting around your pool has already kicked off. Catching it early, before the insects arrive, is far easier than clearing them out after they have settled in.