You bring your horse in from the pasture, and get ready to curry- but the little yellow specks aren’t coming off! It must be that time of year again, botfly season. Depending on where you live, the botfly season can range anywhere from August until late May. Here is what you need to know about bot fly eggs on horses.
What is a Botfly?
A botfly (also known as heel flies or warble flies), is a parasite (Oestridae) that attack mammals. Their larvae live inside animals, and unfortunately, they are common in horses and other livestock. They are best known for their hard-to-remove eggs frequently found on horses’ legs and lower abdomen. The adults look similar to bees and will annoy horses as they attempt to attach eggs to the animal’s hair.
Once a botfly lays eggs, they will be stimulated by your horse’s attempt to remove them or scratch the area. Within the first five days, bots hatch into their maggot form. After the maggots hatch, the larvae enter the horse through the mouth by accidental ingestion or even crawling. Once inside the mouth, maggots will bury themselves in the mouth tissues for around 30 days. The final phase is where problems develop. The larvae will attach to the stomach lining where they then develop into much larger larvae. From here they bury themselves in stomach tissues causing issues. After many months (sometimes up to 10 months), new larvae will release via your horse’s manure and pupate outside the host.
Effects on Horses
Externally, bot flies are an irritant and lay unsightly eggs which are difficult to remove. Internally, large quantities of botflies can cause digestive issues such as constipation, diarrhea, inflammation, ulcers, and loss of appetite. Your horse may lose condition, show signs of stomach irritation, and in very rare serious cases can cause perforation of the stomach.
Treatment & Bot Fly Removal
The entire lifecycle mentioned above is almost one year, providing an opportunity to stop the cycle. Although external insect control is always important, botfly eggs need to be removed. There are specialty tools on the market for egg removals such as bot fly knives and bot stones. However, they can be particularly difficult to remove even with tools. Some owners will opt to clip a horse in affected areas. (You can check out our top-ranked clippers here.)
The next tool in the bot battle is deworming. As a standard, most veterinarians advise horse owners to automatically deworm after the first frost. This is because the temperature typically kills all the egg-laying females. Deworming will kill growing larvae in the stomach, and therefore cannot restart the cycle. However, not all dewormers are effective for every parasite. Currently, moxidectin and ivermectin are approved for botflies.
To manage botflies and other insects or parasites, manure management, and pasture rotation are helpful tools. Regular grooming will also help owners quickly identify, remove, or treat; eggs attached to horses.
Botflies can be a pain but are easily managed and treated. You can read more on deworming schedules here. If you have questions or need assistance in developing a schedule, we recommend consulting your equine veterinarian.
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