Bot Fly Eggs On Horses-Treatment & Removal

Last Updated on December 26, 2022

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 botfly eggs on horses.

What is a Botfly?

A botfly (also known as heel flies or warble flies), is a parasite (Oestridae) that attacks 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, it 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 that 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 following 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.

Does Vinegar Kill Bot Fly Eggs?

One of the keys to managing bots in horses is to remove the eggs that are laid on your horse’s legs. This helps to break the life cycle of the bot and reduces the burden of bots in your horse’s intestines.

You will read many suggestions of how to kill botfly eggs, and vinegar is often named as a good technique to use. But does vinegar kill botfly eggs?

There is no scientific evidence that the vinegar method works to kill botfly eggs, but it may help to loosen the eggs so they can be removed from the coat. Bot fly eggs are remarkably resilient, and the best way to kill them is to scrape them from the coat using a bot knife.

Will Fly Spray Kill Bot Eggs?

Many horse owners regularly apply fly spray to deter flies from landing on their horses. Unfortunately, bot flies do not seem to be put off by these pungent repellents, and will lay eggs on horses regardless of whether they have had fly spray applied or not.

Fly spray does not kill bot fly eggs either, and neither will insecticides. The best method of keeping botfly eggs under control is to remove them with a bot knife, and this can be a daily task during botfly season.

How Big Are Bot Fly Eggs?

Horse bot fly eggs are very small but are just about visible to the human eye. Each egg is around 0.05 inches in diameter – that is just over 1 millimeter for those of you who use the metric system.

Bot fly eggs are quite easy to identify, as they look like flecks of pollen on your horse’s legs. However, try to brush them off, and you will find them firmly stuck in place!

Each female botfly can lay up to 1000 eggs on a horse’s body, and she will use glue to secure each egg to the horse’s coat. The best way to remove botfly eggs is to scrape them off with a bot knife. It is unlikely you will be able to remove every single egg, but keeping them to a minimum will help to minimize the amount your horse ingests.

Are Botfly Larvae Contagious?

Theoretically, botflies can be transmitted to humans, but it is rare. If you are removing bot fly eggs from your horse, take care not to touch your eyes, nose, or mouth. Wash your hands thoroughly after grooming your horse and removing bot flies, taking extra care to remove any dirt from under your fingernails.

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 plan, 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.