Finally caught a great Baetis hatch on the San Juan, and wondered - we could see the fish rising from a high bluff, and they were all in about a 100 square yard area. What I'm curious about is how do the bugs know that that first cold cloudy day is the day to spring for the surface after waiting all this time, and how do the fish know to come from afar(this area does not constantly hold fish) to feed on them?