Flies are drawn to your dog by a combination of body heat, carbon dioxide from breathing, bodily secretions, and odors from skin, ears, or waste. Some flies just want to feed on moisture around your dog’s eyes or nose, while others are after blood. Understanding which signals attract flies helps you figure out whether the problem is normal warm-weather nuisance or a sign of something that needs attention.
What Draws Flies to Dogs
Every time your dog exhales, they release a plume of carbon dioxide. Insects use CO2 as a reliable cue to locate warm-blooded animals, and dogs produce plenty of it, especially after exercise or on hot days when they’re panting. Body heat works the same way, acting as a beacon that flies can detect from a distance.
Beyond these basic signals, dogs produce a rich mix of skin oils, saliva, and secretions around the eyes, nose, ears, and rear end. Nonbiting flies like common house flies and face flies don’t actually pierce the skin. Instead, they feed by sponging up these secretions. Eye gnats, tiny flies only 1.5 to 2.5 millimeters long, specifically congregate around a dog’s eyes to feed on mucus, pus, and blood. Some species are also attracted to the genital area for the same reason.
Moisture is a key factor across the board. Wet fur, drool, discharge from the eyes or nose, and urine-soaked hair all create the damp, odor-rich environment that flies find irresistible. Hot, humid weather intensifies these odors and speeds up bacterial growth on the skin, making the problem noticeably worse in summer.
Types of Flies That Target Dogs
Not all flies bother dogs the same way. The ones you’re seeing likely fall into two broad categories: nonbiting flies and biting flies.
- House flies and face flies don’t bite. They land on your dog to feed on secretions, particularly around the eyes, nose, and any open wound. They’re annoying and can transmit disease, but they aren’t drawing blood.
- Stable flies look almost identical to house flies but have a painful bite. Both males and females feed on blood. They’re especially known for targeting the ear tips of dogs with pointed, erect ears. German Shepherds are a classic example.
- Black flies bite during daylight hours outdoors and can leave swollen, bleeding welts.
- Biting midges (sometimes called no-see-ums) are only 1 to 3 millimeters long, nearly invisible, and deliver bites that are painful relative to their size.
- Horse flies and deer flies are large, up to 3.5 centimeters, and only the females bite. They generally prefer horses and cattle but will feed on dogs when available.
- Sand flies are weak fliers active mostly at night. Females have piercing mouthparts and feed on dogs and humans alike.
If the flies are clustering around your dog’s face without visible bites, they’re likely nonbiting species feeding on secretions. If you’re seeing bloody, crusty ear tips or welts, biting flies are the culprit.
Health Problems That Make It Worse
A healthy, clean dog will attract some flies in warm weather. A dog with an underlying health issue will attract significantly more. Flies are extremely sensitive to the odors produced by bacterial growth, infected wounds, and bodily discharge, so an uptick in fly activity around your dog can be a signal worth investigating.
Ear infections are one of the most common triggers. The yeast and bacteria involved produce a distinct smell that draws flies to the ears, compounding the itchiness and pain your dog already feels. If flies are constantly swarming your dog’s ears, it’s worth checking for redness, discharge, or a foul odor inside the ear canal.
Any moist wound or skin lesion acts as a magnet. Flies are attracted to contaminated wounds, hot spots, or areas where the coat is matted with urine or feces. This is especially concerning because it can lead to fly strike (myiasis), a condition where flies lay eggs directly on the dog’s skin. The larvae that hatch feed on damaged tissue and can cause serious harm quickly. Dogs that are elderly, have limited mobility, suffer from incontinence, or have untreated skin conditions are at the highest risk. Hot, humid weather accelerates the process.
Eye discharge, whether from allergies, infection, or tear staining, gives nonbiting flies and eye gnats exactly the protein-rich meal they’re looking for. Dogs with chronic eye tearing or nasal discharge will consistently attract more flies than dogs without these issues.
Breed and Lifestyle Factors
Your dog’s ear shape matters more than you might expect. Dogs with erect ears, like German Shepherds, tend to get fly bite lesions on the tips of the ear flaps, which are exposed and have thin skin with minimal fur coverage. Dogs with floppy or semi-erect ears develop lesions in different spots: along the folding edge or at the base of the ear where moisture collects.
Dogs that live primarily outdoors are more prone to fly problems than indoor dogs, and the risk increases substantially if they live near livestock. Farms, stables, and areas with animal waste create large fly populations that readily move to nearby dogs. Dogs that are confined outdoors, unable to move away from fly-heavy areas, face the greatest risk of persistent biting and potential fly strike.
Diet plays an indirect role too. Higher-protein or higher-fat diets can produce stronger-smelling waste, which attracts more flies to your yard. If your dog’s stool seems to be a fly magnet, the food they’re eating may be part of the equation. Promptly picking up waste is one of the simplest ways to reduce fly populations around your home.
Keeping Flies Away From Your Dog
Start with the basics: keep your dog clean and dry. Regular grooming prevents matted fur from trapping urine, feces, or moisture against the skin. Clean any wounds promptly and keep them covered or treated. If your dog has chronic eye discharge or an ear infection, treating the underlying condition removes the attractant at its source.
For dogs that spend time outdoors, reducing fly habitat makes a real difference. Pick up waste daily, clean food and water bowls frequently, and eliminate standing water where possible. If your dog lives near livestock or a compost pile, that proximity alone can explain heavy fly pressure.
When it comes to repellents, be careful. DEET, the most common insect repellent for humans, is toxic to both dogs and cats. The ASPCA warns it can cause neurological problems including tremors, seizures, and death. Citronella, often marketed as a natural alternative, comes from a plant that is also toxic to pets. Other plants commonly assumed to be safe repellents, including geraniums, peppermint, lavender, and garlic, can be harmful to dogs if ingested.
Look for products specifically formulated and labeled for use on dogs. Topical treatments containing ingredients approved for canine use can provide a barrier against both biting and nonbiting flies. For dogs with erect ears that are prone to stable fly bites, petroleum-based products applied to the ear tips can create a physical barrier that discourages feeding. Fly-repellent ear tags or bandanas designed for dogs are another option for outdoor animals. The key rule is simple: never use a product on your dog that wasn’t made for them.