This year, international rock flipping day (started in 2007) is September 14th. But you can celebrate every day!
“The point is simply to have fun, and hopefully learn something at the same time. We don’t want to over-determine what that something should be: those of a more scientific frame of mind might focus on IDs or ecological interactions, while those of an artistic or poetic bent could go in a different direction entirely…
Whatever you do, please be sure to replace all rocks that you flip as soon as possible, so as not to disrupt the natives’ lives unduly.”
See this post by Gwen Pearson to learn more. She blogs at Wired.com, with her column “Charismatic Minifauna”. She is a wonderfully witty entomologist, I highly recommend following her pieces.