Bot Flies in Horses

Bot Flies in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
Bot Flies in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What are Bot Flies?

The bot fly looks like a bee with its brown hairy shape and wings. The female lives long enough to lay her eggs then perishes. From the egg stage on the exterior of the body, they enter by way of your horse licking an area where the eggs have been deposited. The licking assists the hatching of the eggs into their larvae form, which spend approximately three weeks developing within your horse’s mouth before traveling to the stomach where they attach to the lining and remain during winter. After ten months, they exit via the feces where they mature into adults.

During the hot summer, bot flies are a constant source of irritation for your horse. They can affect the performance of your horse and his health and wellbeing.

Symptoms of Bot Flies in Horses

  • If you see your horse licking its stomach or legs often it could be because of clumps of eggs or hatched larvae that are irritating them
  • Sometimes your horse may try rubbing its face or try biting strange objects to ease the irritation within its mouth
  • The larvae can cause ulcers within the mouth and surrounding area as they burrow through the skin to get into the mouth
  • Colic may become a problem for your horse as large numbers of larvae in its stomach may cause difficulties
  • Poor appetite and abdominal pain 


  • The common horse bot lays its eggs onto your horse’s body, which are then transferred into the body through the mouth
  • The throat type of fly lays eggs close to the horse’s mouth, such as on the neck or jaw area so that the larvae can gain entry to the body easily via the mouth
  • On rare occasions the nose bot lays eggs around the nasal and lip areas


Causes of Bot Flies in Horses

  • The cycle of the bot fly can be a major irritant to your horse putting him off eating and even spooking him as the bot fly persists in bothering him
  • Without fly control, they can cause severe damage to your horse’s stomach and intestines 
  • The cycle begins when the bot flies lay their eggs on the horse’s haircoat during the spring through to the autumn months
  • When your horse licks an area where the eggs are present, the processes of the licking encourages eggs to hatch and the larvae are ingested 
  • Once inside, the larvae travel to the stomach where they incubate in the stomach lining for ten months before exiting through the feces
  • The infected feces lay in the paddock to reinfect your horse or develop into the bot fly adult and  the cycle continues


Diagnosis of Bot Flies in Horses

Often your horse may seem healthy and unaffected by the bot fly, but severe infestation can cause problems in the mouth area, and within the stomach area. Giveaway signs are coat infestation, inflammation of the mouth area, and colic type conditions. Blockage of the stomach can also occur it the infestation is severe. The diagnosis of this condition is done by your veterinarian examining your horse’s feces by way of a microscope. This examination will show the amount of eggs passed through your horse’s system and allow the specialist to estimate the extent of the condition. 

He will also do a visual inspection of your horse to determine the amount of eggs that are on the body which will provide an accurate diagnosis. These eggs are rather easy to see as they are varying shades of creamy yellow color and they contrast clearly against the deep colors of most breeds of horses. Understanding this yearly cycle can help in prevention for the next season.



Treatment of Bot Flies in Horses

Removal of the eggs is essential to prevent the life cycle of the bots from escalating. Using a tool called a bot knife allows the veterinarian to scrape the eggs off the hide without hurting your horse. The more eggs he can can remove, the less chance of them being ingested by your horse. The veterinarian may suggest additional measures to prevent the laying of the eggs, and that is spraying your horse with a suitable fly spray preparation during the bot fly season. This will not only keep the bot flies away but other pests as well. Deworming medication or parasiticides can assist your horse to move the larvae out of the stomach. 

If your horse is stabled or in a stall, using strong fans during the summer will decrease the population of the bot fly from that area. If you do all you can to reduce the numbers of bot flies it will save you from a severe infestation. Removing all horse droppings from the paddocks and fields will also help reduce the amount of reinfection by your horse. Ensure you keep the manure pile away from key areas of the farm, and especially the barn will help.



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Recovery of Bot Flies in Horses

Management of the bot fly is essential to keep it from becoming a major problem. Repeated infestations can wear the health of your horse down, with emerging ulceration of the gastric lining interfering with digestion, and inflammation in the mouth causing loose teeth. Removing manure from the paddock as often as possible, using a fly sheet on your horse over the worst months of fly bot attacks, spraying with an approved fly spray product and scraping the eggs from your horse will all help. Regular worming treatments keep the bot infestation down as well. Normally your horse can tolerate around 100 larvae or so without it affecting their health, but after that excessive infestation can cause weight loss and in extreme cases, death.



Bot Flies Questions and Advice from Veterinary Professionals

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