By Eleanor Blazer
        Is there a bot running in the background of your horse?

        In the technical world of computers a bot is an automated software program that runs in the background. Equine bots are unwanted parasites.

        The bot fly looks like a small bee.  They can be seen darting around the legs, head and sides of horses. The adult bot fly does not bite, sting or eat - it lives on stored energy.  The bot fly lives only to reproduce.

        As the bot zooms around the horse it lays eggs on the hair.  The eggs are generally yellow in color.  One egg at a time is attached to the hair.

        One bot fly can lay several hundred eggs on a horse.

       There are three types of bot flies that prefer horses. Each "species" has a favorite place to lay eggs.  The "horse bot", which is the most common, targets the legs, flanks and girth area of the horse.  The "nose bot", which is rare, prefers the hairs around the muzzle. The "throat bot" lays eggs on long hairs under the jaw line.

       The buzzing fly can cause some horses to become irritated.  Many riders have been thrown because of a busy bot fly.

       The next step in the bot fly's life cycle is for the egg to be transported to a moist warm environment - your horse's digestive system.  As the horse eats, grooms and rubs his nose on his legs, the eggs become dislodged and some start to hatch.  The eggs and larvae end up in your horse's mouth.  Remaining eggs hatch and the collective larvae live in the mouth for about three weeks - burrowed in the soft tissue of the gums, tongue and lips.  This is called the first instar stage of the life cycle.

        At the end of the instar stage the larvae molt (the second instar stage) and are swallowed.

        The bot fly larvae attach to the lining of the stomach and small intestine.  They use sharp hooks located in their mouth to fasten themselves to the lining of your horse's internal organs. They will remain for about seven to nine months…feeding on your horse.  Bots at this stage can be either second or third instars.

        Once that part of the bot fly life cycle is complete, they pass through the large intestine and are expelled in the manure.  The larvae burrow into the ground.  In the summer and fall larvae pupate and become adult bot flies, mate and lay eggs on your horse…

        Researchers are not in agreement as to how much damage bot larvae can cause.  It is generally accepted that bots are detrimental to the horse's health. 

        During the first instar stage, irritation to sensitive mouth tissue can be present. Infection and the loosening of teeth may occur with high numbers of first instars in your horse's mouth.

        Most veterinarians agree bot infestation can result in poor health, failure to utilize nutrients from feed, colic, loss of appetite, ulcers and abnormal bowel movements.  Rupture of the stomach and blockages of intestine can occur in severe cases.

        But regardless what researchers disagree or agree about - I don't want them on or in my horse!

        The first step in eradicating bots is to eliminate manure piles.  Breaking up piles to expose them to the sun may help kill larvae.  Removing that unsightly manure pile on a regular basis may also help break the life cycle of the bot fly.

        Now to remove the eggs from the hair: daily grooming will aid in detecting eggs when they appear.  You'll find they are well attached.  There are many tools on the market to help remove bots.  Bot knives, grooming blocks, sandpaper, bot combs are examples.  A safety razor will also work.  Be careful when using sharp edged tools.

        You can use warm water and wash the legs.  The warm moisture makes the eggs hatch very quickly.  Use fly spray immediately after washing the legs to kill the larvae.  The first instars do not live long if they don't reach a supporting environment (your horse's mouth).

        Use disposable gloves when removing bot eggs and wash your hands afterward.

        Humans have been infected with horse bots in rare cases.  A warm moist environment causes the eggs to hatch and the larvae can migrate into the human skin.  Do not rub your eyes.  There have been cases of ocular myiasis (invasion of the eye by a parasitic larvae) due to bot eggs.

       When removing the eggs don't do it where you'll contaminate grass, hay or the area where you horse may eat.

        Controlling bot larvae once they're in your horse requires chemicals.  Luckily, products are available that work quite well and are reasonably safe if used according to the directions.

        The anthelmintic (a drug that expels parsites) called ivermectin is the most common chemical used to kill bots living within the equine digestive system.  Ivermectin is available in many over-the-counter horse deworming products.  Even though bots are not "worms", dewormers that contain ivermectin will kill bots in the stomach and small intestine.

        Boticides are recommended to be given after the first hard-killing frost (the adult bot flies are killed) and again in the spring to remove any bots that may still be present in the stomach or large intestine.  Horses that live in warm climates may be exposed to bot flies year around and may need more frequent treatments.  Consult your local veterinarian.

       Daily dewomers do not control bots.  If you use one of these products, be sure to administer a boticide twice a year.

        One note about moxidectin - this chemical is a boticide.  But there is some controversy about the safety of the chemical.  It should not be used on foals under the age of four months, weak horses or horses carrying a heavy parasite load.  Use extreme caution, read the label and consult your veterinarian.




                                    Bot Eggs on the Inside of a Knee                             Close Up of Bot Eggs on Horse Hair      


* For information about horse care take the online course " Stable Management " and " Nutrition for Maximum Performance " taught by Eleanor Blazer.
Earn certification or work toward a Bachelor of Science degree in equine studies.

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