The Yellow Devils - Treating Horses With Bot Flies

Image By Horse&Hound (https://www.horseandhound.co.uk/horse-care/horse-care-tips/qa-all-about-bot-eggs-37720)

When I see a brushstroke of yellow on my horses’ legs, I know it is time to bring out the bot knife to eradicate the devilish eggs. I remember when I got my first one as a girl. An experienced, older rider, older than me at least, gifted me one to scrape off my first bot fly eggs. Though such a gift might seem paltry or dull, to me, it was a wonderful one because, at the time, I felt that I was taking on a serious responsibility of a horse owner, caring for my trusty steed alongside an admired mentor. 

In late summer, equine botflies lay their eggs on the legs, thighs, underbellies, and necks of horses, depending on the species, hundreds of tiny yellow dots that together form clear splashes of sunny color. They need to be scraped off with a bot knife in a place where horses will not graze such as inside the barn on cross ties. The hope of the mother fly is that the horses will be bothered by them, bite at them, and ingest them so that the larvae can grow and feed inside the tongue, mouth, and eventually, the gut. So removal needs to be in a place where horses will not graze or ingest the eggs. 

Once the larvae make it to the intestinal tract, they steal nutrients from the horse to feed and grow. Sometimes, they can even cause ulcers or colic. In Spring, they come out in manure, ready to recommence the cycle. While impossible to kill every bot fly, preventative measures can provide relief to your horses. 

Personally, I find the bot knife to be the easiest and most effective, but people also use very fine-toothed combs designed for small animals as well. The key is to keep a vigilant eye and to remove the eggs as soon as you see them. A daily check-in summer can make a huge difference to your horse. Fly spray, fly sheets, and socks/boots will also deter the botflies and other insects. Pastures and paddocks cleaned daily will also help. In early fall, about a month after the fly season has ended, worming with Ivermectin will kill the larvae. Bots are not worms, but Ivermectin has proven effective in killing them. 

As always, enjoy the privilege and joy of caring for your horses and deter the yellow devils from completing their cycles of life. We will never win the battle entirely, but we can decrease numbers using preventative measures.