Composting organic waste creates soil amendment for gardens but often attracts unwanted insects. Common house flies, tiny fruit flies, and fungus gnats are frequent nuisances. While beneficial species like Black Soldier Flies exist, most people seek to minimize flying pests. Managing flies requires understanding the conditions that make the compost pile an attractive breeding ground. This guide provides practical solutions to prevent and manage fly infestations in your home composting system.
Why Flies Are Drawn to Compost
Flies are drawn to compost because it provides food, moisture, and shelter for laying eggs and developing larvae. Decomposition releases volatile compounds and aromas that signal a rich food source, resulting directly from the breakdown process.
Exposed food scraps, especially nitrogen-rich “green” materials, are a major attractant. Fruit flies are drawn to the sweet, fermenting scents of decaying produce. Scraps left on the surface offer an accessible place for flies to lay eggs, quickly leading to an infestation.
The moisture level is another significant factor in fly reproduction. Excessive moisture creates a conducive environment for fly types like fungus gnats and drain flies. Water-saturated organic matter supports larval survival. Anaerobic conditions, caused by too much water, slow decomposition and create foul odors.
Managing Compost Materials to Prevent Infestation
Optimizing the compost pile is the most effective long-term strategy for fly control. Maintaining the correct ratio of carbon-rich “brown” materials to nitrogen-rich “green” materials is primary for a fly-resistant system. A ratio of approximately two parts brown material to one part green material helps absorb excess moisture and odors.
Properly burying all new food scraps is a key preventative measure. Kitchen waste should be placed deep inside the existing material, ideally six to eight inches below the surface. Covering the scraps with a thick layer of dry brown materials, such as shredded leaves or wood shavings, masks the scent and prevents adult flies from laying eggs.
Controlling the moisture content ensures the environment is less hospitable to fly larvae. The compost should feel consistently damp, like a wrung-out sponge, rather than soaking wet. If the pile becomes too wet, adding absorbent brown materials like shredded newspaper or cardboard restores the balance and prevents anaerobic conditions.
Regularly turning the compost pile accomplishes multiple goals. Aeration introduces oxygen, which accelerates decomposition and helps the pile reach higher internal temperatures. Turning physically disrupts the fly reproductive cycle by disturbing and killing eggs and larvae. Frequent turning drastically reduces the insect population.
Utilizing Active Deterrents and Traps
Employing active deterrents and traps quickly reduces existing adult fly populations. Placing a physical barrier over the compost bin prevents flies from accessing the material. Using a tight-fitting lid or a fine mesh screen blocks entry points and contains odors.
Strategic placement of the bin also serves as a passive deterrent. Flies prefer shaded, moist areas for breeding, so positioning the system in a sunny, well-ventilated location makes the environment less appealing. Increased sun exposure and airflow keep the surface layer drier, discouraging egg-laying.
Certain natural additives can be sprinkled over the top layer to deter flies. Diatomaceous earth (DE) is a physical insecticide that dehydrates and kills flies and their larvae upon contact. A thin layer of wood ash or garden lime can also be applied to dry out the surface and make it less suitable for reproduction.
Simple DIY traps capture adult fruit flies and house flies near the bin. A vinegar trap uses apple cider vinegar in a jar with a drop of dish soap. The soap breaks the surface tension, causing flies attracted to the fermenting smell to sink and drown. Place these traps adjacent to the compost system to reduce adults.