Bot Fly Eggs On Horses-Treatment & Removal

Last Updated on February 1, 2022 by Urska

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.

What is a Botfly


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.)

Wahl Professional Animal Figura Equine Clipper

Bot Fly Eggs on Horses - Wahl

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.

Final Words

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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What wormer kills bots in horses?

Approved over-the-counter dewormers for control of bot-fly larvae are avermectins drugs, such as ivermectin and moxidectin. Ivermectin is know for its efficiency against intestinal and insect parasites; it also kills migrating larvae of the bot-fly. It is available in a variety of formulations, including pour-on, oral tablet, injectable, spot-on, and topical. Moxidectin, which is very effective against adult bot-flies, can be used as an alternative to ivermectin if desired.

What do bot eggs look like on horses?

The adult bot fly look like a scrawny honeybee. They have light hair on the thorax and are yellowish in color. The eggs are small, round, and yellow-orange in color. The adult bot fly attach their eggs to the hairs of the horse’s body. They are very easy to notice, specially when attached to the hairs of a dark-colored horse.

How do you get bot eggs out of a horse’s mane?

Probably the easiest and most common way to get bot eggs out of a horse’s mane is by using a bot knife. The bot knife has a rounded blade with a serrated edge. If you place the knife above the egg and scrape downward, you will remove the egg from the mane. However, pay attention on where the removed eggs land to the ground and make sure for this to happen far from where your horse grazes to prevent the reinfection.

How long does it take for bot fly eggs to hatch?

The bot fly larvae progress through three stages of development. Those three stages are known as instars. The time from egg laying to pupation is the total duration of the first two instars. During this time, the larvae migrate deeper into the tissue of the host. Incubation period within the host can take from 5 to 12 weeks. The third and final instar is known as the prepupal stage. During this final instar, the larva grows into a pupa.

How do you keep bot flies off horses?

The best way to prevent bot flies to lay eggs on your horse is to use some protective measures, such as fly sheets and fly boots. Fly sheets are pieces of material that cover the horse’s back and belly. They help to reduce the likelihood of the bot flies laying eggs on your horse’s underbelly. The fly boots cover the horse’s leg and hoof and protect those areas from bot flies.

Can Bot Flies kill horses?

Bot flies are tiny, horse-killing insects that lay their eggs on the skin of horses. After hatching, the larvae eat away at the skin which can cause an infection. Horses with bot fly infestations will have wounds that appear as a red, irritated rash all over the body. The infested areas of the horse’s skin are usually the neck, chest, and belly. In addition, bot flies are also known to carry diseases that can cause severe damage in the stomach and intestine of your horse if left untreated. The ulceration can potentially cause a breach of the stomach lining, which can be fatal for a horse, although that’s very rare.