(Horseline) EPPS Biting Fly Trap uses dish soap and water to trap and kill flies. Flies are attracted to the large, dark trap because it appears to be a potential host. Most biting flies tend to circle around the host before landing to bite. As flies circle the trap, attempting to fly through the clear deflector panels, they hit the panels and land in the soapy water trays below. Check the trap every few days to strain out dead flies and maintain water level. Requires four 7' T-posts (not included).