# How Long Do Horse Flies Live? Fly Control for Horses Horse flies live roughly three to four weeks as winged adults, though the full life cycle from egg to adult stretches across months. Only the females bite, and they bite hard enough to draw blood from horses and people alike [1]. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Adult horse flies live about 3 to 4 weeks, but larvae develop for 4 to 5 months or longer before becoming adults [1]. - Only female horse flies feed on blood. Males feed on nectar and do not bite [1]. - Horse fly season peaks in midsummer, with most activity from early July to late August in northern regions [2]. - Horse flies can spread disease and cause painful sores, so control matters for your horse's health [3][1]. - The most effective control combines manure management, traps, and veterinarian-approved repellents [3]. ## How Long Do Horse Flies Live? The Life Cycle Explained Horse flies and deer flies belong to a family of large, heavy-bodied flies with powerful wings and very large eyes [1]. They are fast, strong fliers, which is part of why they are so hard to swat. The adult stage is short. A female horse fly lives about three to four weeks, long enough to bite, feed, and lay eggs near open water [1]. Males live a similar span but do not take blood meals [1]. The immature stages last far longer. Females lay eggs in the vicinity of open water, and the larvae develop in aquatic to semiaquatic environments, often buried deep in mud at the bottom of ponds and lakes [1]. These larvae are predatory. They have sharp mandibles and feed on smaller vertebrates and invertebrates, and they can even nip at the toes of people wading in shallow water [1]. Development from larva to adult takes 4 to 5 months, and it takes even longer in low temperatures. Larvae can hibernate through cold weather [1]. That means the horse flies bothering your horse in July may have started their lives the previous fall. Seasonal patterns vary by climate. In one three-year survey of livestock farms, horse flies were collected from early June to late October, with a single peak in late July to early August [2]. In a warmer region, horse flies attacked horses throughout both the dry and rainy seasons, posing a constant threat to health [4]. Wherever you live, expect the pressure to build in warm weather. ## What Horse Flies Do to Horses A horse fly bite is not a minor annoyance. Both the larval stages and the adult flies can inflict pain when they bite [1]. The bite leaves a wound, and repeated bites can create sores on your horse's coat and skin [3]. Horse flies are also vectors. They transmit pathogens as biological and mechanical carriers, which means they can move infectious organisms from one animal to another [2]. This is why fly control is a health measure, not just a comfort measure. Feeding behavior matters for control. In one study of tabanids on cattle, the leg was the most frequent landing site, and the average feeding bout lasted about 2.76 minutes [5]. The same study found significantly more flies active at midday than in the morning or afternoon, and temperature was positively associated with fly abundance [5]. Your horse is most vulnerable during the hottest part of the day. ## Horse Fly Control: A Step-by-Step Plan Good control targets the places flies breed and the times they feed. Work through these steps in order. ### Step 1: Break the breeding cycle Horse flies lay eggs near open water, and their larvae develop in mud and wet ground [1]. You cannot drain every pond, but you can manage the wet areas around your barn and paddocks. Fix standing water from leaky troughs and flooded corners. Keep drainage ditches clear. ### Step 2: Manage manure and stalls Flies of many kinds live in manure. Keep stalls clean and remove manure frequently to control flies [3]. This step also reduces other fly species that bother horses, so it pays off twice. ### Step 3: Remove bot eggs from the coat Remove bot fly eggs from your horse's coat regularly before they hatch into adult flies [3]. A grooming routine with a bot knife or warm cloth handles this. ### Step 4: Use repellents and sprays correctly Many insect sprays and lotions are available for direct application to horses to prevent flies [3]. Ask your veterinarian about the best options for your area, because products differ in what they control and how long they last [3]. Follow the label exactly, and never apply a product labeled for cattle or dogs to your horse without veterinary guidance. ### Step 5: Add physical protection Fly masks, sheets, and leg wraps reduce exposed skin. Since the leg is a common landing site [5], leg protection can make a real difference for horses that stomp and pace. ### Step 6: Consider traps Stationary traps can capture large numbers of horse flies. In one survey, a single commercial trap per farm collected tens of thousands of flies over three seasons [2]. Traps do not replace hygiene and repellents, but they lower the population around your barn. ### Step 7: Time turnout around peak activity Horse flies are most active at midday, and abundance rises with temperature [5]. On hot days, consider stabling your horse during the middle of the day and turning out in the cooler morning or evening hours. ### Step 8: Rotate pastures and manage grazing Rotate pastures with other livestock, such as cows or sheep, to decrease your horse's exposure to specific parasite types [3]. Keep the number of horses per acre low to reduce the shedding of parasite eggs in feces in any one spot [3]. These steps support overall health while you fight flies. For a broader look at managing pests around your horse, see [Fly and Pest Control for Horses](/knowledge/veterinary-medicine/equine-care/horse-fly-pest-control). ## Seasonal Fly Control Calendar | Time of Year | What Is Happening | What to Do | |---|---|---| | Late winter to early spring | Larvae are developing or hibernating in mud and water [1] | Fix drainage, clear standing water, plan supplies | | Late spring | Adults begin emerging, activity starts in early June in northern regions [2] | Start daily manure removal, begin grooming for bot eggs [3] | | Early summer | Fly numbers climb | Set up traps, start repellents, use fly masks and sheets | | Midsummer (late July to early August) | Peak activity in northern regions [2] | Stable horses at midday, check skin daily for sores | | Late summer to fall | Activity continues into late October in northern regions [2] | Keep up control until flies stop | | Year round in warm climates | Horse flies attack in both dry and rainy seasons [4] | Maintain control all year | ## Signs Something Is Wrong Fly bites are visible, but the damage can go deeper. Watch for these signs. - Open sores or scabs on the coat, especially on the legs and belly [3][5] - Constant stomping, tail swishing, head tossing, or pacing - Patchy hair loss or thickened skin where bites cluster - Restlessness that interferes with eating or resting - Weight loss, diarrhea, or colic signs, which can point to parasite problems linked to grazing and pasture management [3] - Eye discharge or squinting if flies are gathering around the face If your horse is losing weight or showing digestive signs, your veterinarian may recommend a fecal egg count. Deworming decisions should be based on those results and your vet's advice. A healthy adult horse with very few or no parasite eggs in its feces might not need deworming more than once or twice a year, while young horses need regular deworming because they are more likely to have parasites [3]. ## Common Mistakes Horse Owners Make **Spraying only when flies are already bad.** Start control in late spring before populations peak [2]. Prevention beats reaction. **Ignoring the legs.** The leg is the most frequent landing site for these flies [5]. If you only spray the topline, you are missing the target. **Skipping manure removal on busy days.** Flies live in manure, and frequent removal is a core control step [3]. A few skipped days can undo weeks of work. **Using the wrong product.** Insect sprays and lotions vary widely. Talk to your vet about the best options for your area instead of guessing [3]. **Forgetting bot eggs.** These eggs hatch into adult flies if you leave them on the coat [3]. Regular grooming removes them before that happens. **Turning out at midday in summer.** Fly abundance is highest at midday and rises with temperature [5]. Shift turnout to cooler hours when you can. **Assuming one method is enough.** Traps, hygiene, repellents, and physical protection work best together. No single tool solves the problem. ## Supplies and Setup That Matter A few practical items make daily control easier. - A sturdy manure fork and a covered manure bin placed away from the barn - Fly masks, sheets, and leg wraps sized to your horse - A bot knife or grooming stone for egg removal [3] - A commercial horse fly trap rated for your property size [2] - Veterinarian-approved sprays and lotions, stored per label directions [3] - A simple drainage plan for troughs, gutters, and low spots Set up your routine so it takes minutes, not hours. Clean stalls daily, groom daily, and check your horse's legs and belly for new bites. If you keep other animals, plan pasture rotation with them in mind [3]. If you are thinking about your horse's long-term care alongside fly management, [How Long Do Horses Live? Lifespan and Senior Care](/knowledge/veterinary-medicine/equine-care/horse-lifespan) covers what to expect as your horse ages. ## Limitations and When to Contact a Veterinarian No control plan eliminates every horse fly. Traps, sprays, and hygiene reduce the population, but flies can travel from neighboring properties and from natural water sources you cannot manage [1]. Expect some bites even with excellent care. Contact your veterinarian the same day if your horse has a bite wound that is swelling, hot, or draining pus, or if your horse is stomping so much that it is lame. Call right away if you see hives, facial swelling, or difficulty breathing after bites, since allergic reactions can worsen quickly. Schedule a routine visit if your horse has ongoing weight loss, diarrhea, or colic signs, or if skin sores are not healing [3]. Your veterinarian can check for parasites with a fecal egg count and recommend a deworming plan based on the results [3]. Individual cases need a veterinarian. Your horse's age, health history, and local fly pressure all affect the right plan, and only your vet can examine your horse and give specific advice. ## Frequently Asked Questions ### Do horse flies bite humans too? Yes. Female horse flies feed on vertebrate blood, and both the larvae and adults can inflict painful bites on people as well as animals [1]. Larvae in shallow water have even nipped at the toes of wading humans [1]. ### Are horse flies worse at certain times of day? They are most active around midday. One study found significantly more tabanids on cattle during midday compared with morning and afternoon, and temperature was positively linked to fly numbers [5]. Turnout in the cooler hours can reduce bites. ### Can horse flies spread disease to my horse? Yes. Horse flies act as biological and mechanical vectors of several pathogens, which makes them a health concern beyond the bites themselves [2]. This is one reason control is worth the effort. ### Do all horse flies bite? No. Only the females feed on vertebrate blood [1]. Males do not take blood meals, though they are still part of the population you are managing. ### Does climate change the fly season where I live? It can. In one region, the appearance of dominant horse fly species shifted about one month earlier compared with data from the 1980s, likely due to warming temperatures [2]. In warm climates, horse flies can attack in both dry and rainy seasons [4]. Start control earlier if your springs are warming sooner. ## Related Articles - [How Long Do Horses Live? Lifespan and Senior Care](/knowledge/veterinary-medicine/equine-care/horse-lifespan) - [Fly and Pest Control for Horses](/knowledge/veterinary-medicine/equine-care/horse-fly-pest-control) - [How Long Do Labs Live](/knowledge/veterinary-medicine/clinical-methods/how-long-do-labs-live) - [Horse Fly Bites and Horse Bites: Treatment and Care](/knowledge/veterinary-medicine/equine-care/horse-fly-bites-and-bites) - [How Long Can Fleas and Ticks Live Without a Host?](/knowledge/veterinary-medicine/parasitic-diseases/fleas-ticks-without-host) - [How Long Do Horses Eat a Day? Normal Grazing Behavior](/knowledge/veterinary-medicine/equine-care/how-long-horses-eat-daily) - [Gasterophilus intestinalis in Horses: Equine Bot Fly Larvae Infestation of Stomach Walls and Control Strategies](/knowledge/parasites/livestock-parasites/gasterophilus-intestinalis-equine-bot-fly-larvae-stomach-walls-control) ## References 1. [Horse Flies and Deer Flies - Integumentary System](https://www.merckvetmanual.com/integumentary-system/flies/horse-flies-and-deer-flies). Merck Veterinary Manual. 2. [A temporal analysis of horse fly prevalence in Tokachi, Hokkaido, Japan, based on a 3-year entomological survey](https://pubmed.ncbi.nlm.nih.gov/40991565/). Journal of medical entomology, 2025. 3. [Horse Parasites and Flies - Horse Owners](https://www.merckvetmanual.com/horse-owners/routine-care-of-horses/horse-parasites-and-flies). Merck Veterinary Manual. 4. [Tabanidae (Diptera) collected on horses in a Cerrado biome in the state of Tocantins, Brazil](https://pubmed.ncbi.nlm.nih.gov/39016348/). Revista brasileira de parasitologia veterinaria = Brazilian journal of veterinary parasitology : Orgao Oficial do Colegio Brasileiro de Parasitologia Veterinaria, 2024. 5. [Direct Observation of Feeding Behavior of Adult Tabanidae (Diptera) on Beef Cattle from Khon Kaen Province in Thailand](https://pubmed.ncbi.nlm.nih.gov/39194807/). Insects, 2024. ## Further Reading - [Merck Veterinary Manual: Horse Owners](https://www.merckvetmanual.com/horse-owners)