We were in Costa Rica as part of our PC cruise in Feb. '05. We were on a "Pontoon Boat Jungle Ride" excursion on a river with rain forest on both sides of us. The guide said not to worry about mosquitos because they didn't come out before 5:00 PM. We didn't see any bugs except butterflies/dragonflies. We did see a line of long-nosed bats resting on the underside of a palm tree overhanging the river. They get active when the mosquitos do so they can chow down on them.