The Three Stages of a Bot Fly Invasion in Your Horse

Last Updated on March 8, 2022 by Allison Price

The female bot fly, or Gasterophilus intestinalis ), hovers around horses in spring and deposits between 150 to 1,000 tiny, yellow-colored eggs around their necks, legs, noses, and muzzles. Within five days of the eggs being placed, the eggs hatch into maggots when they are stimulated by your horse biting, licking, or even biting them. This is the first stage in the bot fly’s evil plan.

The bodily invasion is the second phase. This involves the larvae crawling to the horse’s mouth, or being ingested. They then burrow into the gums and tongue. They then lie in wait for about a month.

Bot Fly Invasion in Your Horse

The bot fly’s third and most dangerous phase is the one that takes over your horse’s stomach. This is the point in movies where you notice a character acting differently. You start to notice something that is a little…off. Larks attach mostly to the stomach lining in the non-glandular area, or the upper part of the stomach. Surprise! — they hatch into one-half to three-quarters-of-an-inch long larvae with narrow, hooked mouths that allow them to attach to the lining of the stomach and intestinal tracts. They attach to the stomach tissue, digging into it, causing all kinds of problems for your horse. This makes them an alien host for the botfly for the next 8-10 month. After almost a year of rent in your horse’s stomach, the larvae then pass in your horse’s manure, pupate in soil for 3-5 months, and then emerge as adults ready for another alien invasion.

It’s pretty gross, isn’t it? The thing is, while the whole life-cycle can be quite disgusting (and horsemen are always horrified to see the yellow-grey eggs), bot flies pose a serious risk to the horse’s health.

How bot flies can harm your horse’s health

Three basic types of gazterophilus exist.

  1. intestinalis: that lay eggs mainly on the forelegs or shoulders.
  2. haemorrhoidalis which lay black eggs on horse’s lips. They can then crawl to horse’s mouth.
  3. nose: which lay eggs on the jaws or throat-latch regions.

The three types all follow the same pattern: hatching, migration, attachment to the stomach mucosal membrane, and then attaching to it. Only one thing is different between them. Where They attach. They can attach to each other. Do you do it? The bot flies will buzz around your horse trying to lay eggs and alarming you (and the horse) as they do so. The real problem begins once they are ingested.

  • Dental problems: When the larvae enter your horse’s mouth, it hangs there for a while, burrowing into his gums, causing severe irritation, pus pocket formations, and possibly even loss of teeth. You may notice a loss in your horse’s appetite or interest in eating.
  • Sinus infections in horses: Horses might also begin releasing mucus from the noses to combat larvae.
  • Problems with the gastrointestinal tract: When larvae enter the stomach and attach to it, there can be swelling, ulceration, and discharge. Gastritis is the general term for irritation or inflammation of the stomach line. This is usually a sign of an underlying condition, such as a bot fly infestation .
  • Compromise nutrition:Larvae eat nutrients that are beneficial to the horse’s stomach and gut lining, which can lead to a loss of weight.
  • Colic or blockages: Horses can withstand small infestations of larvae but they can become physically blocked if large numbers accumulate in the stomach. These larvae can be half-inch to three quarters of an inch long. These physical blockages could lead to impaction.
  • Loss of appetite, weight loss, changes in body condition, hair coat, behavior, or cribbing: These symptoms are all possible signs of gasterophilus infections.

Diagnose and Treatment of Gasterophilus Horse Infection

You may be scratching your head at the last bullet point. This laundry list of symptoms could be due to many foregut or hindgut conditions. It is difficult to use these symptoms as a definitive indicator of gasterophilus infection. Your vet will not be able to diagnose an infection without difficulty. The best way to diagnose an infection is to examine the horse’s feces and identify larvae. This will indicate that your horse has had an infection for several months. This is not ideal.

Although reducing parasitic burden is good for horses, it won’t fix the damage they do to the digestive system.

You can treat a gasterophilus infestation in horses by using anthelmintics or dewormers. This will help to rid your horse’s system of the parasites.

While reducing the parasitic load can be beneficial for your horse, eliminating the parasites will not heal any damage they have left in the digestive system. An fecal test will help determine the extent of parasitic infection in your horse. No matter how severe the infection is, it’s best to focus on your horse’s overall digestive health.

These are some ways to improve your digestive health.

Bot Fly Infection Prevention in Horses

You can help your horse stay healthy and in good health because of the high rate of gasterophilus infection. You can take the “prevention of death” route and spray your horse with insecticide to prevent bot flies landing on your horse. Remember that the eggs only last a few days before they hatch, and you have to keep them away from your horse. Bot eggs may choose to host a human, but this is rare. Always Wash your hands after removing bots and Avoid touching your eyes while you are scraping off the eggs.

Good pasture management is also a great way to reduce the number of bot fly populations. Manure should be removed from pastures and paddocks regularly. It is important to compost properly before it is spread on fields. This will help kill the bot fly and other parasite eggs. This helpful fact sheet is from the University of Connecticut to learn more about horse manure management.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!