Farnam Equi-Spot® Spot-On Fly Protection for Horses protects horse from flies, gnats, mosquitoes and ticks. Kills & repels house flies, stable flies, face flies, horn flies, eye gnats, and ticks. Applied once every two weeks, it provides long-lasting control against dangerous ticks that can spread Lyme disease and mosquitoes that may transmit West Nile Virus and Equine Encephalitis, as well as biting flies and gnats. It won't wash off in the rain or when your horse sweats. Ideal for pastured horses.