Prozap Fly-Die Ultra is a hard-hitting, long-lasting water-based formula that protects horses from stable flies, horn flies, house flies, horse flies, deer flies, face flies, gnats, ticks, lice, and mosquitoes, including those that may transmit the West Nile virus. This sweat and water-resistant formula binds to the hair shaft providing up to 14 days of protection even after heavy workouts and rain. In the pasture, on the trail, or in the show pen, Prozap Fly-Die Ultra protects your horse from rain or shine.