# Dog and Flies: Fly Strike and Bite Relief A fly problem on your dog almost always shows up first as one of two things: an irritated, crusty ear tip or nose from biting flies, or a wound that suddenly has maggots in it. The first thing to check is the skin itself. Part the fur, look at the ear tips, the bridge of the nose, and any wound or soiled area, and look for small raised bumps, hair loss, crusts, or moving larvae. If you see maggots, this is an emergency and your dog needs a veterinarian the same day. Flies are not just a summer nuisance. They feed on blood, they lay eggs on moist skin and open wounds, and in some species their larvae burrow into living tissue. The medical term for larval infestation of a live animal is myiasis, and the everyday term is fly strike. Fly strike is different from fly-bite dermatitis, and the two problems need different responses. This article explains how to tell them apart, what to do at home, what a veterinarian will do, and how to keep flies off your dog. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## The Two Main Fly Problems in Dogs Owners often use "fly strike" for any fly-related skin problem. In practice, veterinarians separate two conditions. ### Fly-Bite Dermatitis Biting flies such as the stable fly, Stomoxys calcitrans, feed on blood and cause painful skin lesions. In dogs, the classic pattern is necrotic dermatitis at the tip of the ears [1]. The skin becomes thickened, hairless, crusted, and sometimes ulcerated. This is an irritant and allergic reaction to repeated bites, not an infection with larvae. The lesions are usually on the pinnae (ear flaps), especially the tips and edges, and sometimes on the nose or face. Dogs with upright ears and dogs kept outdoors are more exposed. The condition is sometimes called fly-bite dermatitis or fly dermatitis. ### Fly Strike (Myiasis) Fly strike is the infestation of living tissue with fly larvae, commonly called maggots. Female flies lay eggs on wounds, on soiled fur, or on moist skin, and the eggs hatch into larvae that feed on tissue, secretions, or wound debris [2]. Some species lay eggs on intact skin and the larvae burrow in, while others target open wounds. Myiasis can be cutaneous (in the skin and wounds), or it can involve other sites. Cases have been reported in the ear canal, prepuce, toes, and vagina of dogs [3]. Rare cases involve the urinary tract or intestine [4][2]. The common thread is that larvae are feeding on the dog. Fly strike is more likely in dogs that cannot groom or move normally. Debilitated, elderly, or long-haired dogs, and dogs with open wounds, urine or fecal soiling, or skin folds, are at higher risk [5]. Puppies also appear more affected in some surveys [6]. ## Why Flies Target Some Dogs More Than Others Several factors make a dog more attractive to flies or more vulnerable to infestation. - Open wounds. Flies lay eggs on wound edges, and larvae then consume living tissue. This is the pattern with the New World screwworm, Cochliomyia hominivorax, which can be fatal if untreated [7]. - Soiled or matted fur. Urine, feces, and moisture in long coats create an ideal egg-laying surface. - Reduced mobility or grooming. Dogs that cannot turn to clean themselves, or that are recumbent, accumulate soiled fur. - Outdoor housing and warm weather. Fly activity is seasonal, and shelter dogs and outdoor dogs are repeatedly exposed [3]. - Ear disease or skin folds. Discharge and moisture in the ear canal or skin folds attract flies. A retrospective study of 59 dogs in Hong Kong with Old World screwworm myiasis found that all cases recovered with a combination of larval removal and wound debridement, antibiotics, and topical and systemic insecticides [8]. That outcome depends on early treatment. Delay allows larvae to destroy more tissue and, in some species, to cause systemic illness. ## How to Tell Fly-Bite Dermatitis from Fly Strike The table below is the fastest way to sort out what you are looking at. Use it as a starting point, then confirm with a veterinarian. | Fly problem | Visible signs | How to confirm | Action | |--|--|--|--| | Fly-bite dermatitis | Hair loss, crusts, thickening, and dark necrotic skin on ear tips, nose, or face. Dog may shake head or scratch. | Visual inspection of ear tips and nose. Look for the pattern of lesions, not larvae. | Clean gently, protect the area, and ask a veterinarian about a licensed fly repellent or insecticide. A topical imidacloprid and permethrin spot-on reduced lesion scores in a controlled study [9]. | | Cutaneous myiasis (fly strike) in a wound | Maggots visible in or around a wound. Wound may be enlarging, foul-smelling, or bleeding. Dog may be painful or depressed. | Direct visual examination. Larvae may be deep in the wound. | Emergency. Do not wait. A veterinarian removes larvae, debrides the wound, and starts appropriate treatment. | | Furuncular myiasis (boil-like nodules) | Firm, raised nodules with a small opening, often on the trunk or limbs. One or more larvae inside. | Visual examination and gentle probing of the opening. | Veterinary treatment. A single dose of afoxolaner killed larvae of Dermatobia hominis and Cordylobia anthropophaga in field studies [10][11]. | | Ear canal myiasis | Head shaking, odor, discharge, and maggots in the ear canal. | Otoscopic examination by a veterinarian. | Urgent veterinary care. Larvae must be removed and the ear treated. | | Soiled-fur strike | Maggots in matted fur around the rear, tail base, or skin folds. Skin underneath may be inflamed or ulcerated. | Part the fur and inspect the skin. | Urgent veterinary care. Clip the fur, remove larvae, and treat the skin. | | Fly worry or annoyance | Dog is restless, stamping, biting at flanks or ears. No skin lesions yet. | Observation of fly activity around the dog. | Environmental fly control and a veterinarian-approved repellent. | If you are unsure whether you are seeing maggots or just debris, look for movement and for the segmented, worm-like shape of larvae. Maggots are usually pale and clearly segmented. Do not try to dig deep into a wound yourself. ## What Happens During Fly Strike: The Mechanism Understanding how fly strike develops helps you act early. 1. A fly finds a target. The target is a wound, a moist skin fold, or soiled fur. Some flies, such as Cordylobia anthropophaga, can infest skin even without an obvious wound [5]. 2. Eggs are laid. Flies lay eggs on or near the target. In warm weather, eggs can hatch within hours. 3. Larvae feed. The larvae feed on tissue, wound secretions, or debris. In screwworm myiasis, larvae consume living tissue and enlarge the wound [7]. 4. The wound worsens. Tissue damage, inflammation, and secondary bacterial infection follow. The dog may become painful, febrile, and depressed. 5. Systemic illness can develop. Severe or untreated myiasis can cause toxemia and, in screwworm cases, death [7]. This is why fly strike is an emergency, not a wait-and-see problem. The flowchart below shows the decision path when you find a fly-related skin problem on your dog. ```mermaid flowchart TD A[Find skin problem on dog] --> B{See maggots} B -->|Yes| C[Fly strike emergency] B -->|No| D{Ear tip or nose lesions} D -->|Yes| E[Fly bite dermatitis] D -->|No| F{Wound or soiled fur} F -->|Yes| G[Inspect for hidden larvae] F -->|No| H[Consider other skin disease] C --> I[Go to veterinarian now] G --> I E --> J[Vet visit for diagnosis and repellent] H --> J I --> K[Larvae removed and wound treated] J --> L[Prevention plan started] ``` ## Diagnosing Fly Problems in Dogs A veterinarian diagnoses fly problems mainly by looking. The history matters too: where the dog lives, whether it is outdoors, recent wounds, and whether the dog has been able to groom. ### Physical Examination The veterinarian examines the whole dog, not just the visible lesion. Fly strike can hide in the ear canals, between the toes, under the tail, and in the prepuce [3]. The coat is parted and the skin inspected. Larvae are identified by their appearance, and in some cases by molecular methods [4][2]. ### Lesion Scoring For fly-bite dermatitis, veterinarians may score lesions by extension, alopecia, crusts, scales, erosions, ulcers, loss of substance, and lichenification. This is how treatment response is measured in clinical studies [9]. You do not need to score lesions at home, but it helps to photograph the area so you can tell whether it is improving. ### When Larvae Are Found If larvae are present, the veterinarian assesses the depth and extent of the wound, checks for systemic signs such as fever, and decides whether the dog needs hospitalization, wound debridement, antibiotics, or systemic antiparasitic treatment. In a study of 76 dogs and cats with screw-worm myiasis, the most common sites in dogs were the external ear canals, the perineum, and the medial canthus of the eye [12]. These are easy places to miss on a quick look. ## Treating Fly-Bite Dermatitis Fly-bite dermatitis is treated by stopping the bites and letting the skin heal. ### Removing the Fly Pressure The single most important step is to keep flies off the dog. This means environmental control and, where appropriate, a veterinary-recommended insecticide or repellent. In a controlled study, a single topical application of imidacloprid 10% and permethrin 50% on the head and ear bases reduced fly dermatitis lesion scores in treated dogs, while untreated control dogs did not improve [9]. This is a licensed product for dogs, and it is not appropriate for cats. ### Wound and Skin Care Crusted, necrotic ear tips need gentle cleaning and protection. Do not pick at the crusts. Your veterinarian may recommend a topical treatment and may clip hair around the lesions to reduce moisture and fly attraction. Secondary bacterial infection may need antibiotics. ### What Not to Do Do not apply human insect repellents, essential oils, or permethrin products labeled for dogs onto cats in the household. Permethrin is toxic to cats. Do not use any product on a dog without checking the label and your veterinarian, especially if the dog is pregnant, nursing, or very young. ## Treating Fly Strike (Myiasis) Fly strike treatment has two parts: removing the larvae and treating the wound and the dog. ### Manual Removal The first step is mechanical removal of larvae. In a case report of a dog with a deep gluteal wound, 216 maggots were removed by forceps, and the wound was sponged and disinfected with 70% alcohol and povidone-iodine solution [13]. This gives you a sense of the scale. A small-looking wound can contain a large number of larvae. Manual removal alone may not get every larva, especially deep in tissue. This is why systemic treatment is often used alongside removal. ### Systemic Antiparasitic Treatment Modern isoxazoline antiparasitics have strong larvicidal activity against myiasis-causing flies. - Afoxolaner. A single oral dose killed 100% of Dermatobia hominis larvae within 24 hours in naturally infested dogs [10]. In a field study of Cordylobia anthropophaga, parasiticide efficacy was 94% on Day 15 and 100% on Day 30, and all treated dogs were parasite-free by Day 30 [11]. Against Cochliomyia hominivorax, afoxolaner killed all larvae within 24 hours [7]. - Lotilaner. A single oral dose produced a larval expulsion rate of 80.5% at 2 hours and 93.0% at 6 hours in dogs infested with Cochliomyia hominivorax [14]. - Spinosad, spinosad with milbemycin, and nitenpyram. In a comparative study, nitenpyram killed all larvae at 6 hours and spinosad with milbemycin at 7 hours. Afoxolaner and spinosad alone killed all larvae within 24 hours. Milbemycin alone left two cases with live larvae at 24 hours [15]. These are prescription decisions. Your veterinarian will choose a product based on the species of fly, the severity of the infestation, the dog's age and health, and whether the dog is already on a preventive. Do not give a dog an antiparasitic that was prescribed for another animal. ### Wound Care and Support After larvae are removed, the wound is cleaned and debrided. Antibiotics are often needed because fly larvae contaminate wounds with bacteria. In the Hong Kong case series, all 59 dogs recovered with larval removal and wound debridement, antibiotics, and topical and systemic insecticides [8]. In a Colombian report, two stray dogs with Cochliomyia hominivorax infestation were treated with manual removal, repellents around the wounds, and antibiotics, and one dog needed eye enucleation because of severe tissue damage [16]. That outcome shows why early treatment matters. ### Hospitalization Dogs with extensive wounds, fever, dehydration, or systemic illness may need hospitalization for intravenous fluids, pain control, and wound management. Fly strike can cause toxemia, and severe cases can be fatal if untreated [7]. ## A Step-by-Step Diagnostic Sequence for Owners If you find a fly-related skin problem, work through these steps. 1. Look for maggots. Part the fur and inspect the wound, ear canals, toes, tail base, and skin folds. If you see larvae, go to a veterinarian now. 2. Check the ear tips and nose. Hair loss, crusts, and thickened skin in these areas point to fly-bite dermatitis. 3. Check for soiled fur. Urine or fecal staining around the rear or in skin folds attracts flies and hides larvae. 4. Note the dog's general condition. Lethargy, loss of appetite, fever, or pain suggests systemic illness and needs urgent care. 5. Photograph the area. This helps you and your veterinarian track change over time. 6. Do not apply random products. Wait for veterinary guidance, especially if you have cats. 7. Start prevention. Once the acute problem is treated, keep flies off the dog. ## Preventing Fly Problems in Dogs Prevention is easier than treatment, and it is especially important for dogs at higher risk. ### Environmental Fly Control Reduce fly numbers around the dog's living area. Remove standing water, clean up feces promptly, and manage garbage and decaying organic matter. Fly traps and screens help. If your dog lives outdoors, provide a clean, dry resting area away from fly breeding sites. ### Coat and Skin Management Keep the coat clean and dry. Clip matted fur, especially around the rear and in skin folds. Bathe soiled dogs promptly. Long-haired and double-coated breeds benefit from regular grooming during fly season. A clean, dry coat is much less attractive to egg-laying flies. ### Wound Care Cover or manage open wounds. Any wound on an outdoor dog should be checked daily for larvae. This is especially true in warm weather. If a wound is not healing, have it evaluated. ### Veterinary-Recommended Insecticides and Repellents Your veterinarian can recommend a licensed product for fly control. The imidacloprid and permethrin spot-on used in the fly dermatitis study is one option for dogs [9]. Isoxazoline products used for flea and tick control also have larvicidal activity against myiasis-causing flies [10][11][7][14]. If your dog is already on a monthly isoxazoline, ask your veterinarian whether it provides useful protection against the flies in your area. ### High-Risk Dogs Dogs that are elderly, debilitated, incontinent, or unable to groom need daily checks during fly season. This includes dogs with mobility problems, dogs recovering from surgery, and dogs with chronic skin disease. Check the ear canals, perineum, prepuce, toes, and any skin folds. Early detection is the difference between a simple treatment and a major wound. ## When Fly Strike Becomes an Emergency Fly strike is not a cosmetic problem. Larvae feed on tissue, and the damage can progress quickly. Seek emergency care if you see any of the following. - Maggots in a wound, ear canal, or soiled fur - A wound that is enlarging, bleeding, or foul-smelling - Fever, lethargy, loss of appetite, or vomiting - Pain when the area is touched - A dog that is recumbent or unable to groom - Multiple nodules with small openings on the skin Do not wait to see if the larvae go away. They will not. Do not try to flush a deep wound with household chemicals. Cover the area loosely if needed and transport the dog to a veterinarian. ## Limitations and When to Contact a Veterinarian This article is educational and is not a substitute for veterinary diagnosis or treatment. Individual dogs vary in their risk, their underlying health, and the fly species in their environment, so a veterinarian needs to examine your dog to make a diagnosis and choose treatment. Contact a veterinarian promptly if: - You see maggots anywhere on your dog - Your dog has a wound that is not healing or is getting worse - Your dog has hair loss, crusts, or thickened skin on the ear tips or nose that is not improving - Your dog is lethargic, not eating, or has a fever - Your dog is elderly, debilitated, or unable to groom and has soiled fur - You are unsure whether a skin lesion is fly-related If your dog has a known fly-bite dermatitis and the lesions are spreading or the dog is uncomfortable despite home care, a recheck is warranted. Your veterinarian may adjust the treatment plan or check for other skin diseases that can look similar. ## Frequently Asked Questions ### Can flies lay eggs on my dog in just a few hours? Yes. Flies can lay eggs on moist skin, wounds, or soiled fur within hours, and eggs can hatch quickly in warm weather. This is why daily checks matter for high-risk dogs during fly season. ### What is the difference between fly-bite dermatitis and fly strike? Fly-bite dermatitis is an irritant and allergic reaction to fly bites, usually on the ear tips and nose, with hair loss and crusts. Fly strike is myiasis, where fly larvae actually infest and feed on the dog's tissue or wound. ### How do I remove maggots from my dog? Do not attempt deep removal at home. A veterinarian removes larvae manually, often with forceps, and uses a systemic antiparasitic to kill larvae that remain in the tissue. Home removal can leave larvae behind and damage the wound. ### Are there medications that kill fly larvae in dogs? Yes. Afoxolaner, lotilaner, spinosad, spinosad with milbemycin, and nitenpyram have all shown larvicidal activity against myiasis-causing flies in dogs. These are prescription decisions, so ask your veterinarian which product is right for your dog. ### Is fly strike contagious to other pets or to people? Myiasis is not spread directly from dog to dog. It occurs when flies lay eggs on a susceptible animal. Some fly species that cause myiasis in dogs can also affect humans, so good hygiene and fly control matter for the whole household. ### Which dogs are most at risk of fly strike? Dogs with open wounds, soiled or matted fur, reduced mobility, or debilitation are at highest risk. Long-haired dogs and dogs kept outdoors during fly season are also more vulnerable. ### Can fly-bite dermatitis be cured? Yes. Fly-bite dermatitis improves when flies are kept away from the dog and the skin is allowed to heal. A veterinarian can recommend a licensed insecticide or repellent and treat any secondary infection. ### When should I go to the emergency clinic? Go immediately if you see maggots, if a wound is enlarging or foul-smelling, or if your dog is lethargic, feverish, or not eating. Fly strike can cause systemic illness and can be fatal if untreated. ## Related Articles - [Equine Fly Sheets, Masks, and Boots: UV Blocking, Insect Mesh Density, and Sweet Itch Relief](/knowledge/veterinary-medicine/equine-and-farm/equine-fly-boots-eczema-sheet) - [Why Does My Bird Bite, and How to Stop It](/knowledge/veterinary-medicine/pet-bird-care/bird-biting-solutions) - [Fly and Pest Control for Horses](/knowledge/veterinary-medicine/equine-care/horse-fly-pest-control) - [Dairy Farm Fly Control](/knowledge/animal-farming/dairy-cattle/dairy-farm-fly-control) - [Chicken Flight Capabilities: Why They Fly and How to Manage It](/knowledge/veterinary-medicine/backyard-poultry/chicken-flight-capabilities-why-they-fly-and-how-to-manage-it) - [Dog Scratches Ear Then Bites Foot](/knowledge/veterinary-medicine/behavior/dog-scratches-ear-then-bites-foot) - [Myiasis Disease: Fly Strike and Larval Infestation](/knowledge/veterinary-medicine/parasitic-diseases/myiasis-disease-fly-strike-and-larval-infestation) - [Black Flies: Bites, Risks and Pet Protection](/knowledge/veterinary-medicine/parasitic-diseases/black-flies-bites-risks-and-pet-protection) - [Rattlesnake Bite in Dogs: Emergency First Aid](/knowledge/veterinary-medicine/emergency-and-first-aid/rattlesnake-bite-in-dogs-emergency-first-aid) ## Sources 1. 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