The presence of circling flies on an outdoor patio quickly transforms a relaxing space into a source of frustration. These persistent insects are not merely an annoyance; their presence indicates a nearby source of moisture or decaying organic matter that serves as a breeding site. Achieving a fly-free environment requires a systematic approach focused on identifying the specific species and eliminating the underlying attractants fueling the population.
Identifying the Type of Nuisance Fly
Successful fly management begins with accurately identifying the species causing the disturbance, as different types are drawn to distinct breeding environments. Three small flies commonly bother patio occupants. Fungus gnats, often mistaken for tiny mosquitoes, are dark, slender insects with long, spindly legs that exhibit weak, erratic flight patterns near potted plants or moist soil. They are poor fliers and tend to hover close to the growing media where their larvae feed on fungi and decaying roots.
Drain flies, also called moth flies, have a distinct fuzzy, moth-like appearance, light gray or tan coloring, and wings with a dark border. These insects thrive in dark, damp conditions, typically emerging from drains, sewer access points, or areas where organic sludge accumulates in plumbing near the patio. Larger species, such as house flies, are attracted to exposed food, garbage, or animal waste and are far more agile in flight. Observing the fly’s appearance and primary location provides the necessary information to target the correct source of the infestation.
Eliminating the Underlying Attraction Sources
The most effective strategy for long-term relief involves eliminating the breeding grounds and food sources that attract these pests. Flies are consistently drawn to areas offering moisture, warmth, and organic material, making sanitation and moisture control paramount. Addressing standing water is an immediate priority, as even small amounts in pet bowls, plant saucers, or clogged gutters can serve as nurseries for various fly species.
For fungus gnats, the focus must shift to potted plants, which become ideal breeding sites when overwatered. Allowing the top one to two inches of soil to dry out completely between waterings removes the moist environment that the larvae require for survival. The inclusion of water-retaining materials like peat moss in patio potting mix can exacerbate gnat problems by keeping the soil perpetually damp.
Proper sanitation of garbage and recycling containers is equally important to deter larger flies like house flies. All trash receptacles near the patio should have tightly sealing lids, and the bins themselves must be cleaned regularly to remove residual food waste and gunk that serve as a breeding substrate. Waiting until the evening before collection to place kitchen scraps into outdoor bins, particularly during warm weather, can limit the amount of time flies have access to the material.
Specific attention should be paid to any exterior plumbing or drainage access points near the outdoor area. Drain flies breed within the gelatinous biofilm that coats the inside of pipes, sinks, and overflow drains. Regularly cleaning these areas with an enzymatic or microbial drain cleaner breaks down the organic sludge and eliminates the larval habitat. Pet waste must also be removed immediately, as decaying excrement is a primary attractant and breeding ground for many filth flies.
Quick Solutions for Existing Fly Populations
While source elimination is the long-term solution, several immediate actions can reduce the existing adult fly population and make the patio usable. One simple and effective physical measure is the use of large oscillating fans. Flies are relatively weak fliers and actively avoid strong air currents, making a fan pointed across the seating area an effective barrier.
Targeted physical traps offer another immediate means of population reduction. Sticky traps, often yellow, are effective for capturing weak-flying insects like fungus gnats, and can be placed directly into potted plants or hung near the affected areas. For flies attracted to fermented material, a simple DIY trap consisting of a shallow dish of apple cider vinegar mixed with a few drops of dish soap can be employed. The acetic acid in the vinegar attracts the flies, and the soap breaks the surface tension of the liquid, causing them to sink.
For more targeted treatment of larval populations in soil or standing water, Bacillus thuringiensis israelensis (Bti) products can be applied. Bti is a naturally occurring bacterium that is species-specific, targeting only the larvae of flies, gnats, and mosquitoes without harming beneficial insects or mammals. These products, often sold as granules or dunks, release the bacterium when wet. The larvae consume it, perishing within 24 hours. Essential oils, such as citronella, lemongrass, and eucalyptus, are also known to repel flies and can be diffused or used in candles to offer localized, temporary relief.