Swimming pools, even when chemically treated, attract various insects from the surrounding environment. These invaders may view the pool as a surrogate pond, a source of hydration, or a beacon of light at night. Understanding which insects are drawn to this habitat and the specific risks they pose is the first step toward effective management. The presence of common aquatic guests often signals a need for small changes in water conditions or maintenance practices.
Common Pool Invaders
The most frequently encountered swimming insects are categorized as “true bugs” (order Hemiptera), including the water boatman and the backswimmer. Water boatmen (family Corixidae) are small, oval-shaped insects that swim right-side up, using their long hind legs like oars. They are primarily herbivores, consuming algae and organic material in the water.
Backswimmers (family Notonectidae) are often confused with water boatmen but have a distinct, triangular cross-section and swim on their backs. They are predatory insects, often feeding on smaller aquatic insects, including water boatmen. Another common sight is the predaceous diving beetle (family Dytiscidae), which has a smooth, streamlined body and uses its fringed hind legs for propulsion.
Finally, mosquito larvae, known as “wigglers,” appear as small, wriggling forms. They hang head-down at the water’s surface to breathe through a specialized siphon tube.
Identifying Potential Harm
Water boatmen are harmless to humans and cannot bite or sting. Conversely, backswimmers are known to deliver a painful, defensive bite if trapped against the skin or mishandled. This bite is often described as a sharp sting similar to that of a bee.
The larvae of the diving beetle, often called “water tigers,” are also predatory and can bite. They use sharp mandibles to inject digestive enzymes into their prey. Mosquito larvae pose no direct threat to swimmers, as they do not bite. The concern from wigglers is their eventual maturation into adult mosquitoes, which are vectors for serious illnesses such as West Nile virus, Zika virus, and dengue fever.
Why Pools Attract Aquatic Insects
Pools primarily attract aquatic insects due to the presence of an accessible food source, algae. Water boatmen are drawn to feed on algae and other microscopic organisms, and they will lay their eggs in the algal growth. Backswimmers follow quickly, as they are predators that feed on water boatmen and mosquito larvae.
Many aquatic insects are strong fliers and are drawn to the pool at night by artificial light, mistaking the illuminated surface for a body of water. Insects are most attracted to light in the cooler, shorter wavelengths of the spectrum, such as blue and white light. The pool’s water also acts as a source of hydration, luring many types of insects to the immediate area.
Effective Removal and Prevention Strategies
The most effective long-term strategy for keeping a pool free of insects is maintaining proper water chemistry to eliminate their food source. This involves regularly testing and adjusting the chlorine and pH levels, aiming for a pH range between 7.2 and 7.8, which prevents algae from flourishing. Applying chlorine shock treatments quickly oxidizes contaminants and kills algae spores, removing the primary attractant.
Physical Removal
Physical removal should be performed daily, using a fine-mesh skimmer to scoop out insects. Use a brush to dislodge any algae or eggs clinging to the pool walls and floor before vacuuming. For persistent mosquito larvae, a targeted treatment such as a larvicide containing Bacillus thuringiensis israelensis (Bti) can be used. This naturally occurring bacteria is toxic only to mosquito and midge larvae.
Lighting and Barriers
To deter flying insects, consider replacing white or blue lighting with warmer hues like yellow or amber LEDs. These warmer lights emit less attractive ultraviolet light. Consistently using a pool cover when the pool is not in use acts as a physical barrier, preventing insects from landing, drinking, or laying eggs.