yay cicadas!
So the East Coast experience contains many aspects, one of which is the lovely "chirping" of tons o' cicadas. Looking up cicada on wiki, I found that the "magicicada" species has a life cycle of 17 years - all spent underground except for a few days where they all come out and mate. The interesting thing is that having the 17 year cycle gives it an advantage over predators on 2 and 3 year cycles, because 17 is prime. Apparently they can also revert to a 13 year cycle, coming out of the ground 4 years early, also prime. Crazy mathematical evolution.