In some regions, early fall brings a bumper crop of bot flies, and with them a rash of bot fly eggs that you'll want to remove. Larvae that matured inside the horse and exited via manure in the spring are now hatching into flies. In the next step in their life cycle, these flies will lay eggs on strategic locations on a horse. When he licks the eggs they hatch, a new generation of larvae enters his mouth and the process is repeated.
You most likely deworm your horse against bots to kill the internal larvae, but you can further diminish their numbers by removing eggs before they have a chance to hatch.
Bot eggs are sticky and yellowish, shaped like small grains of rice. They are commonly deposited on the knees and forearms up to the chest. The eggs can be removed using on of two tools.
On option is a bot knife, which has a rounded blade with a serrated edge. Place the knife above the egg and scrape downward. The egg will fall to the ground, so be sure to do this far from where your horse grazes.
You can also use a porous fiberglass bot block, which can also aid in shedding out a horse. When the block's edge is rubbed over the coat, it "grabs" the eggs. To clean the block itself and create a new sharp edge, scrape it across a hard surface, keeping in mind that you will be leaving bot eggs on that surface.