As the summer heat sets in, you may notice more flies buzzing around your home trying to escape the sweltering outdoors. This begs the question – do flies actually like air conditioning? If you don’t have time to read on, the quick answer is: Generally no, flies do not like air conditioning and will try to avoid direct cold airflow.

However, they are attracted to the warm, humid conditions that air conditioning units can create.

In this nearly 3000 word article, we will explore in depth the complex relationship between flies and air conditioning. We will cover key topics like: their preferred temperatures, why certain areas around air conditioning units attract them, what temperatures or conditions actually deter them, and finally some tips on managing flies around air conditioned spaces.

Flies Prefer Warm and Humid Environments

Ideal Temperature Range for Flies

Flies thrive in warm environments and prefer temperatures between 70-90°F. This warm climate allows them to remain active and breed rapidly. At cooler temperatures below 50°F, flies become lethargic and unable to fly. They may even die off if temperatures drop below freezing.

The optimal temperature for fly growth is between 75-86°F. Within this range, flies can complete their life cycles from egg to adult most efficiently. Warmer temperatures allow flies to grow and develop faster.

For example, house flies can complete their life cycle in just 7-10 days at 86°F compared to 20-30 days at 70°F.

Flies also favor temperatures at the higher end of their range. Studies have shown that house flies reared at 86°F grew larger and produced 50% more offspring than flies reared at 70°F. The warmer climate simply accelerates their breeding and growth.

Humidity is Key

In addition to warmth, flies require ample humidity in order to thrive. Low humidity causes flies to lose moisture rapidly and become dehydrated. Flies prefer relative humidity levels between 45-65%. This moist environment helps their soft bodies retain water.

Humidity is especially important during fly development. Eggs, larvae, and pupae all need sufficiently humid conditions to hatch and mature properly. If the humidity drops below 30%, fly eggs may fail to hatch entirely.

Once flies reach adulthood, higher humidity also supports their activity and breeding. The moist air keeps their bodies from drying out so they can remain lively and lay more eggs. This is why flies swarm around moist decaying matter.

Why Flies Gather Around Air Conditioning Units

Attracted to Exterior Condensation and Drip Areas

Flies, especially house flies, are often attracted to the condensation and water accumulation that forms around the exterior of air conditioning units (1). As air is cooled, water vapor condenses on the cold external coils and metal casing of the unit.

This forms beads and drips of water that fall and collect into puddles below the unit.

Flies need moisture to survive and are attracted to sources of water for drinking and laying eggs. The condensation from air conditioners provides an ideal wet spot for flies to congregate during hot, dry weather.

Some fly species like fungus gnats are also drawn to the damp, fungus-friendly conditions around AC drip areas.

Besides drinking and breeding in the condensate, flies may also be attracted to food particles and organic matter caught in the water. Bits of leaves, dust and pollen settle on the cold AC surfaces and get washed into the drainage area below, allowing flies to find nutrients.

Exterior AC condensation can attract dozens to hundreds of flies at a time, creating frustrating fly problems for homeowners. Fixing leaky condenser drain lines and cleaning away algae growth and debris from AC units can help reduce fly attractions.

Interested in Attic and Duct Areas

In addition to gathering around exterior AC units, flies may also congregate around indoor vents and openings linked to attics and ductwork. This is because attics can provide ideal warm, protected environments for flies to breed and nest.

Access to attics is gained through openings at roof vents, gable vents, eave gaps, and cracks around cables, ducts or pipes. Flies enter the attic to lay eggs in insulation, dust, lint and other accumulated organic debris. The larvae hatch and feed here until emerging as adult flies.

Flies attracted to the attic then follow odor trails and airflow to find their way into the occupied areas of the home. They emerge from bathroom fan vents, range hood vents, heating/cooling ducts, and any gaps around attic access holes or dropped ceilings.

Fly populations multiply rapidly in attics during summer months. A female house fly can lay up to 500 eggs in her lifetime, producing thousands of flies in just a couple of weeks (2). Blocking attic entry points and installing fly light traps can help control attic-bred flies.

Air Conditioning Conditions That Deter Flies

Direct Cold Airflow

Flies generally dislike cold conditions. Air conditioners that blow out cold air create an unfavorable environment that deters flies from frequenting the area (Terminix). The cold airflow makes it difficult for flies to function properly, disrupting their ability to feed, rest, or reproduce.

Studies show that temperatures below 80°F drive flies away, with direct cooling between 50°F to 60°F being the most effective at fly control (Entomological Society of America). So, crank up that AC unit this summer and enjoy fewer flies buzzing around!

Dehumidified Air

In addition to cold, dehumidified air also hampers flies. Air conditioners remove moisture from indoor air, creating an environment too dry for flies to thrive. Houseflies require humidity levels above 45% to engage in normal activity like feeding and mating (PennState Department of Entomology).

Dehumidified indoor air causes flies to lose moisture from their bodies, leading to dehydration and interference with reproductive processes. This is why flies flock to humid areas and can be a nuisance in bathrooms or kitchens.

Use of a dehumidifier along with an AC unit provides a formidable one-two combo against flies!

Advanced Air Filtration Technologies

Some modern central air conditioning systems also utilize enhanced air filtration methods that further discourage flies. High-efficiency particulate absorbing (HEPA) filters can remove up to 99.97% of allergens and fine particles from the air (EPA).

This ultra clean indoor environment gives flies fewer places to hide and breed. Other advanced technologies like ultraviolet germicidal irradiation (UVGI) use UV light to deactivate microbes and fungi.

By targeting fly food sources and breeding grounds, these filtration methods cut off lifelines for flies. While pricier, upgraded central AC units with such features provide powerful fly control and cleaner indoor air.

Tips for Managing Flies with Air Conditioning

Keep Units and Surrounding Areas Clean

Flies are attracted to filth, so keeping A/C units and the nearby areas clean is crucial. Remove any standing water, debris, or food particles around the external A/C condenser using a hose, brush, or vacuum. Then spray the zone with an EPA-approved disinfectant.

Doing this weekly blocks fly access to breeding grounds and food sources.

Check A/C filters monthly and replace dirty ones so dust and dander don’t accumulate. Dust buildup inside ductwork also appeals to flies, so have HVAC professionals deep clean the system annually.

Install Fly Screens on Units

Fly screen material secured over A/C wall units, windows, or ventilation ducts provides a physical barrier preventing flies from entering alongside the air flow. Opt for rust-proof aluminum, bronze, or stainless steel screening for durability and longevity.

Screen Material Opening Size
Aluminum 1/32 inches or 0.8 mm
Bronze, Stainless Steel 1/16 inches or 1.6 mm

The small openings block entry but allow air flow. Have screens custom fabricated to fit each A/C access point.

Use Fans to Disrupt Fly Zones

Flies tend to hover in areas protected from wind and weather. Strategically placed fans disturb their preferred habitats and air streams push them away. Position an oscillating fan near the A/C condenser outside. Inside, mount fans directly over entryways or where flies gather.

The air turbulence confuses flies and foils landing attempts.

Outdoor fans must be waterproof and have protective casing. Choose reliable brands like Vornado, Lasko, or Honeywell. Document fly zones before installing fans. Check weekly to see if fans eliminate hover spots. Continue relocating and adjusting as needed.


To summarize, while flies are attracted to the warm, humid peripherals of air conditioning units, most flies do not directly enjoy being in cold, dehumidified, filtered airflow. By understanding what draws them in and what deters them, you can better control flies with strategic use of air conditioning and other deterrents.

With a diligent prevention approach, you can enjoy a fly-free, cool summer indoors.

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