Bot flies lay sticky pale yellow eggs on horse’s hair, usually on the forearms belly and chest. Adult bot flies lay their eggs on horses in the fall in the northern hemisphere. The flies do this instinctively.
A basic part of the bot’s life cycle requires that the horse bite at and swallow the eggs. The eggs hatch into larvae that over-winter attached to the lining of the horse’s stomach.
Bots are not thought to be very harmful to horses unless they infest a horse in high numbers. However, bot eggs that pepper the hair coat is aesthetically undesirable.
In late fall and winter moxidectin and ivermectin dewormer treatments kill bot larvae in the stomach, an important means of control. However, it is preferable to remove bot eggs before they are ingested, to reduce the number of larvae in the stomach.
Bot eggs are notoriously difficult to remove. They are extremely sticky and adhere well to the hair.
I recommend removing bot eggs in two steps. First, use hot water and a sponge to loosen the eggs. Then use a bot knife to scrape them off. A bot knife has a rounded, serrated edge. When it is firmly run down the limb, it scrapes off the bot eggs.
You may prefer to use a bot block (a porous fiberglass block) which is another means to scrape off bot eggs. It is also useful as a shedding tool.
Tips for safety & Success
It is worth investing in a bot knife or bot block for this procedure.