Bot flies lay eggs on horses, which hatch and migrate to the stomach or small intestine. They can cause irritation, colic, and mouth ulcers. Removing the eggs or using Ivermectin paste can prevent infestation.
Bot Flies, or Oestridae, are small, hairy flies that are often mistaken for bees. They become problems when your horse becomes a host for their larvae. Mature midges will lay their eggs on your horse’s legs, shoulders, or around the mouth by injecting their eggs similar to a bee about to sting. Your horse will show the same concern when he hears them buzzing as he would when bees are present.
Bot eggs appear on your horse as tiny sticky yellow specks. Hundreds of eggs can be laid in minutes. The eggs on your horse’s legs hatch when stimulated by his licking and are carried to his mouth by his tongue. When the eggs around its mouth hatch, the larvae migrate into its mouth. The young larvae then take three weeks to reach your horse’s stomach or small intestine. During this time, they are protected from the effects of antiparasitic drugs.
Bot flies lay their eggs in late summer to early fall. The larvae attach themselves to the lining of your horse’s stomach and small intestine and will feed for up to seven months before they mature. This irritation alone can cause significant problems. At their point of maturity, bot flies will detach and drop, leaving raw areas that are susceptible to further damage from stomach acids. In large numbers, bot fly larvae can disrupt the digestion process and cause your horse to colic.
Once the midges have reached maturity, they will migrate to the surface of your horse’s skin and exit. This site will look like a lump but it is not painful. Migrating bot flies can also cause canker sores and mouth ulcers.
It’s best to remove bot fly eggs as soon as you notice them. Using a bot knife or grooming stone, gently remove each of the small yellow dots from your horse. Your horse will appreciate this easy, if tedious, task as eggs are irritating.
Another option is to stimulate the bot fly’s eggs to hatch by rubbing the area with a washcloth dipped in warm water. Wash the area thoroughly as soon as they are released. During the bots removal process, you can get infected, so be vigilant with your task.
At the start of cooler weather or after the first frost, worm your horse with an Ivermectin paste. The syringe will indicate the dosage based on your horse’s weight. If you have had a lot of bot flies during the season, it is advisable to deworm again after six weeks. This will ensure that you have not lost any of the larvae that were in transit and have yet to be established in your horse’s digestive tract.