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Foot traffic accompanies air traffic, as human visitors carrying red flashlights walk the Little River Trail to observe synchronous fireflies in their annual mating ritual in the Great Smoky Mountains National Park's Elkmont Campground outside Gatlinburg, Tenn. on Tuesday, June 3, 2014. Fireflies' peak flashing lasts about two weeks. This photograph was made by 'stacking' 123 long exposures shot over a 1.5 hour period. (AP Photo/Knoxville News Sentinel, Adam Lau)