Farnam Equi-Spot Spot On Protection for Horses by Farnam Equi-Spot Spot On Protection for Horses FeaturesWon't wash off in rain or when your horse sweatsApplied every 2 weeks to provide control against dangerous ticks that can spread Lyme disease, mosquitoes that may transmit West Nile Virus and Equine Encephalitis, as well as biting flies and gnatsProtection lasts for up to 14 daysIdeal for pastured horsesAvailable in a 6- or 12-week supply . .