Blow flies, the metallic green or blue flies that buzz loudly around trash and animal waste, are attracted to decaying organic matter where they lay eggs that hatch into maggots within 24 hours. Getting rid of them naturally comes down to three things: eliminating what attracts them, blocking their entry, and using plant-based repellents or traps to deal with the ones already around. No pesticides required.
Remove What Attracts Them First
Blow flies track down rotting protein by smell. The key compounds they follow are sulfur-based chemicals released by decaying flesh and organic waste. Research published in Current Biology found that a single sulfur compound from decomposing matter can attract blow flies even without any visual cues. That means if something is rotting on your property, blow flies will find it regardless of where it’s hidden.
The most common breeding sites in residential areas are household food waste and pet feces. Start with these steps:
- Seal garbage tightly. Place food scraps in plastic bags and tie them shut before putting them in outdoor bins. Loose waste in an open trash can is an open invitation.
- Pick up pet waste daily. Dog and cat feces are prime egg-laying sites. Don’t let it accumulate in your yard.
- Check for dead animals. A mouse in the wall, a bird under a deck, or a rodent in the attic will produce a sudden swarm of blow flies. If you notice a cluster of them in one room, follow them to the source.
- Clean trash cans with enzyme-based cleaners. Blow fly larvae produce enzymes called lipases and proteases that break down fats and proteins. Residue left inside trash bins after the bag is removed still contains enough organic material to attract flies. Enzyme-based cleaners break down the same types of compounds and eliminate the odor.
If you compost, maintenance matters. According to the University of California’s Integrated Pest Management program, compost piles must be turned periodically to promote internal heating and rapid decomposition. Piles that sit undisturbed stay cool and moist on the surface, which is exactly where blow flies lay eggs. You can also spread thin layers of organic matter to dry fully in the sun rather than letting it sit in a wet heap.
Block Entry Points
Standard window and door screens with 18 to 20 holes per inch block blow flies effectively. Their bodies are 4 to 7.5 millimeters wide, far too large to squeeze through properly maintained mesh. The problem is usually not the mesh itself but gaps around it. Check for torn screens, loose frames, and spaces where the screen meets the frame. Weatherstripping or caulk around screen mounting points and door frames closes the gaps flies exploit.
Keep doors closed during peak activity, which is during warm daylight hours. Blow flies are most active in temperatures between 70 and 85°F and are strongly attracted to light, so an open door on a sunny afternoon pulls them straight inside.
Essential Oils That Actually Work
Not all essential oils are equally effective, but lab testing on closely related flies shows real results. A 2024 study in the journal Insects tested eucalyptus, fennel, and sage essential oils against flies and found that all three repelled over 87% of flies. Sage was the strongest repellent, blocking 94% of flies at the lowest concentration tested.
For practical home use, mix 15 to 20 drops of eucalyptus, sage, or fennel essential oil with water in a spray bottle and apply around doorways, windowsills, and trash areas. You’ll need to reapply every few hours since the volatile compounds evaporate. Soaking cotton balls in the oil and placing them near entry points or in problem areas gives a longer-lasting effect. Eucalyptus was the most potent overall in the study, achieving the highest kill rate at lower concentrations than the other two oils.
Grow Plants That Repel Flies
Several common herbs produce aromatic compounds that blow flies avoid. Basil is one of the most effective. Planted next to doors or in containers on a porch, it creates a zone flies tend to stay away from. Bay leaf, mint, lemon balm, catnip, and tansy all have similar repellent properties. Tansy also deters ants, fleas, and moths.
One useful trick: periodically brush your hands across these plants or move the containers around. Physical disturbance brings natural oils to the surface of the leaves and releases more of the compounds that flies dislike. A pot of basil sitting untouched in a corner will work, but one you jostle regularly works better.
Build a Simple Fly Trap
A homemade trap can reduce the number of blow flies already on your property. Cut a plastic bottle in half, invert the top to create a funnel, and place it inside the bottom half. Fill the base halfway with a mixture of water and something sweet, like sugar water, overripe fruit, or a splash of fruit juice. Flies enter through the funnel opening and can’t find their way back out.
For blow flies specifically, adding a small piece of raw meat or fish to the bait makes it far more effective than sugar alone. Blow flies are carrion feeders, so protein-based attractants draw them in more reliably than sweet liquids. Place these traps outdoors, away from doors and windows. You want to pull flies away from your house, not toward it. Empty and refresh the bait every two to three days before it becomes a breeding site itself.
Parasitic Wasps for Ongoing Problems
If blow flies are a recurring issue, particularly around livestock areas, hobby farms, or rural properties, tiny parasitic wasps offer a biological solution. A species called Nasonia vitripennis is only 1 to 1.5 millimeters long (barely visible) and targets blow fly pupae specifically. Female wasps locate blow fly pupae buried in soil or hidden under debris, lay their eggs inside, and the wasp larvae consume the developing fly. Each parasitized pupa produces 10 to 40 new wasps instead of a blow fly.
These wasps are harmless to humans, don’t sting, and won’t enter your home. You can purchase them from biological pest control suppliers. They’re most useful in situations where blow flies breed continuously, like near composting operations or animal enclosures, rather than for a one-time indoor problem.
Why Speed Matters
Blow fly eggs hatch into maggots within 24 hours of being laid. The larvae feed aggressively, pass through multiple growth stages in days, then burrow into soil or dry material to pupate. In warm conditions, the entire cycle from egg to adult fly takes as little as two weeks, meaning a small problem becomes a large one fast. Whatever method you choose, acting within the first day or two of noticing blow flies makes control dramatically easier than waiting a week.