Bot flies make horses miserable every year. Nine species of bot flies target horses, mules and donkeys during warm weather, three of which are in North America. If you live in states with mild winters, you may experience bot flies year round. Preventing them not only will make your horse comfortable, but also will improve his health. Bot flies can cause serious diseases that can harm or even kill your horse.
Bot flies look like honey bees but don't have stingers. Instead they lay their egg, called nits, on the horse's hair. When a horse licks or bites an area, it stimulates the nits to hatch, and the larvae burrow into the horse's mouth and tongue. After about a month, the larvae travel to the stomach and intestine, where they grow and mature. When fully grown in about a year, they pass out the horse's intestine in the feces and begin their life as pupae for one to two months, eventually becoming bot flies and starting the cycle again.
Bots can cause colic, severe anemia, ulcers, pus pockets in the mouth, peritonitis, perforated ulcers, blocked intestines, stomach ruptures and perforations, esophageal paralysis and squamous cell tumors.
Grooming your horse to remove the nits is only somewhat effective. Use a sharp-toothed tool, like a metal curry comb or sweat scraper, to scrape the nits from the hair. You also can use warm water and insecticide that's effective on bot fly larvae, and wash your horse's legs to cause the larvae to hatch. The insecticide will kill the larvae. Wear gloves and do not touch your face because bot fly larvae can burrow into your skin too, even if you aren't the right host.
Applying external insecticides once a week on bot areas, such as the legs, belly, and around the mouth (being careful not to get it in the mouth), can help reduce bots and keep the bot flies from laying eggs during peak laying times. Ask your veterinarian what insecticides she recommends to keep bot flies away from your horse. Always consult an experienced veterinarian regarding the health and treatment of your pet.
Over-the-counter dewormers can kill bot larvae. Horse owners frequently use avermectins (ivomectrin) to control bot flies and other parasites. Your veterinarian can recommend the appropriate insecticide and application.
Removing manure will help control bot flies. If you remove the manure before the pupae can mature, you can break the bot fly cycle and eliminate bot flies from that manure.