No single product eliminates every type of outdoor fly, so the best approach combines a skin repellent with some form of area protection. DEET and picaridin are the most effective topical options for most biting flies, while spatial devices and traps handle the nuisance flies buzzing around your patio or picnic table. Here’s what actually works, what doesn’t, and how to layer your defenses.
Topical Repellents: DEET vs. Picaridin
The CDC recommends four active ingredients for skin-applied insect repellents: DEET, picaridin, IR3535, and oil of lemon eucalyptus. Of these, DEET and picaridin are the heaviest hitters against biting flies.
Picaridin performs roughly as well as DEET against mosquitoes, black flies, biting midges (no-see-ums), and chiggers, but without some of DEET’s drawbacks. DEET can damage plastics, synthetic fabrics, and watch crystals. Picaridin doesn’t. It also feels less greasy on skin. Products with lower picaridin concentrations (around 5 to 10 percent) cover mosquitoes and biting flies, while higher concentrations (20 percent) add tick protection to the label.
For DEET, concentrations up to 30 percent are considered appropriate for adults. Higher percentages don’t repel better; they just last longer before you need to reapply. A 20 to 30 percent DEET product typically provides several hours of protection per application.
One important caveat: neither DEET nor picaridin works well against horse flies, deer flies, greenheads, or snipe flies. According to entomologists at the University of New Hampshire Extension, no topical repellent reliably deters those species. If horse flies are your main problem, physical barriers like long sleeves, hats, and mesh clothing are more effective than anything you spray on your skin.
Oil of Lemon Eucalyptus: The Plant-Based Option
If you prefer avoiding synthetic chemicals, oil of lemon eucalyptus (OLE) is the strongest plant-based repellent with EPA registration. Its active compound, PMD, provided protection times similar to low-concentration DEET products in controlled studies. That means it works, but you’ll likely need to reapply more often than you would with a 20 or 30 percent DEET formula.
OLE is not the same as lemon eucalyptus essential oil, which is a common point of confusion. The repellent version is a refined extract with a higher concentration of the active compound. Products labeled “oil of lemon eucalyptus” or “p-menthane-3,8-diol” on the ingredients list are the ones that have been tested and registered. Plain essential oils sold for aromatherapy haven’t gone through the same efficacy testing and generally provide much shorter protection windows.
Spatial Repellents for Patios and Decks
Topical repellents protect your skin. Spatial repellents protect an area by releasing insecticide into the air around you. These are useful when you’re sitting in one spot, like on a deck or around a campfire.
Thermacell devices are the most popular option in this category. They heat a synthetic pyrethroid that disperses into the surrounding air, creating a zone where flying insects are repelled or knocked down. They work best in calm conditions. Wind scatters the active ingredient and shrinks the protected area significantly, so they’re ideal for sheltered patios and less effective on breezy lakeshores.
Mosquito coils operate on the same principle, burning a slow-release pyrethroid into the air. They’re inexpensive and widely available, but the smoke can be irritating, and like Thermacell devices, they lose effectiveness in windy settings. Clip-on devices that use a battery-powered fan to disperse metofluthrin (another spatial repellent) offer a portable alternative. In laboratory testing, metofluthrin both repels and kills flying insects, though real-world performance varies with conditions.
For any spatial repellent, placement matters. Position the device upwind of where you’re sitting so the breeze carries the repellent toward you rather than away.
Fly Traps for Outdoor Dining Areas
Traps don’t repel flies. They attract and capture them, which makes them a good complement to repellents rather than a replacement. Baited traps work best against houseflies, fruit flies, and gnats, the non-biting nuisance species that swarm around food and trash.
Commercial bag traps use a liquid attractant that lures flies into a container they can’t escape. You can also make an effective version at home with a plastic bottle, apple cider vinegar, and a drop of dish soap. The vinegar draws flies in, and the soap breaks the surface tension of the liquid so they sink and drown. Sweet-smelling baits like old wine, sugar water, or overripe fruit also work well.
The key to using traps effectively is placing them where flies already gather, near trash cans, compost bins, or pet areas, and away from where you’re actually sitting. A trap placed right on your dining table will pull more flies toward your food before capturing them. Set traps 15 to 20 feet away from your seating area so they intercept flies before they reach you.
Permethrin for Clothing and Gear
Permethrin is a synthetic insecticide you spray on clothing, not skin. It binds to fabric fibers and remains active through multiple washes. When a fly, tick, or mosquito lands on treated clothing, permethrin disrupts its nervous system, causing it to fall off or die. This is especially useful for outdoor workers, hikers, and campers who face sustained exposure to biting flies over hours.
You can buy pre-treated clothing or spray your own gear with a permethrin product designed for fabrics. Treat shirts, pants, socks, and hats, then let them dry completely before wearing. Combining permethrin-treated clothing with a DEET or picaridin product on exposed skin gives you the most complete protection available.
Layering Your Approach
The most effective outdoor fly control isn’t one product. It’s a combination tailored to your situation. For a backyard barbecue, a Thermacell device on the table plus a couple of baited traps near the trash cans handles most nuisance and biting species. For hiking or working outside, a 20 percent picaridin spray on exposed skin and permethrin-treated clothing covers the broadest range of threats.
Environmental cleanup also makes a real difference. Flies breed in organic waste, so removing standing water, keeping trash sealed, and cleaning up pet waste reduces the local population over time. Citronella candles, ultrasonic devices, and wristband repellents have consistently performed poorly in independent testing and aren’t worth the money.
Safety Tips for Skin Repellents
All EPA-registered repellents go through safety testing, but proper use still matters. Don’t apply them over cuts, sunburned skin, or irritated areas. Avoid spraying directly on your face. Instead, spray your hands first, then rub the repellent onto your face while avoiding your eyes, ears, and mouth. When you head indoors, wash treated skin with soap and water, and launder treated clothing before wearing it again.
For children, follow the concentration and age guidelines on the product label. Oil of lemon eucalyptus products are not recommended for children under three years old. DEET and picaridin products designed for kids typically use lower concentrations and should be applied by an adult rather than letting children handle them directly.