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Bot Flies in Horses: Symptoms & Prevention

Your horse may be affected by various pests when outdoors. Bot flies are a common pest that can cause problems. Our Ocala vets can tell you about the symptoms of bot flies and how to prevent this parasite from infesting your horse.

What Are Bot Flies?

Bot flies can cause internal and external discomfort for horses, although they are not the most harmful parasite.

The main external irritation from bot flies is caused by their large size and their habit of laying eggs in a horse's hair.

While they do not bite horses, they create irritation by landing and walking around to deposit their eggs

Types of Bot Flies

Here are the three types of bot flies we see on horses:

Common Bot Flies

The eggs of common bot flies are yellowish-gray and typically attached to the end of a horse's hair, where they can be reached during grooming or itching.

When the eggs hatch, the larvae enter the horse's mouth and travel to the stomach, where they remain attached to their hook-like mouth for the winter before being expelled in feces in the spring.

After a month in the soil, adult flies emerge and lay up to 500 eggs per week to continue the cycle.

Throat Bot Flies

Throat bot flies lay whitish-yellow eggs near the horse's skin, with the female laying up to 500 eggs like the common bot fly.

After hatching in 3-5 days, the larvae crawl along the jaw, enter the mouth, and settle in the horse's gum line. This can cause pockets and discomfort for the horse.

The larvae mature, move to the stomach for the winter, and are expelled in the spring to start the lifecycle again, similar to the common bot fly.

Nose Bot Flies

Nose bot flies lay brownish-black eggs in the hair around a horse's nose and can lay up to 160 eggs at once.

These flies can be very irritating as they lay their eggs one at a time.

The eggs hatch in just two days, and the larvae burrow into the lip and tongue, eventually moving to the stomach after 5-6 weeks to continue the lifecycle like other nose bot flies.

Symptoms of Bot Flies on Horses

Some of the signs and symptoms of a bot fly infestation that may be noted in horses are:

  • loss of condition
  • impeded digestion
  • increased body temperature
  • restlessness
  • kicking at the belly
  • loss of appetite
  • intermittent diarrhea
  • constipation

Bot flies can also potentially cause more severe issues such as gastritis, stomach ulcers, and, more rarely, peritonitis, which is an inflammation of the membrane lining the abdominal cavity and can be fatal.

How to Treat Bot Flies in Horses

Breaking the year-long lifecycle of bot flies is crucial for successful treatment.

The first step is to remove all bot fly eggs from the horse daily. Next, deworming medication is needed to eliminate the larvae in the stomach.

Your vet can guide you in managing the timing and dosage of the medication for effective treatment.

How to Prevent Bot Flies in Horses

One of the easiest ways to prevent bot flies in horses is through effective sanitation of the area your horse spends their time. 

Here are some of the things you can do to help reduce the possibility of bot flies infesting your horses:

  • Manure should be routinely cleaned up and properly composted. The heat generated during the process will kill the larvae of bot flies.
  • Proper pasture management, including frequent mowing and chain harrowing.
  • Utilize rotational grazing and allow livestock to graze a pasture between horses if possible.
  • Avoid feeding your horses from the ground.
  • Water Clean water, free of feces contamination, should be provided year-round.
  • Monitor your horse and keep up with egg removal as they are spotted.
  • Ensure you keep your horse on a regular deworming program to minimize risk.

You should also have fecal exams performed on your horse regularly to monitor for signs of parasitic infections, including bot flies.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Have you noticed the signs of bot flies on your horse? Book an appointment with our Ocala vets today to discuss treatment and preventive measures. 

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