I was watching a math documentary and one example was a Cicada in North Carolina that only emerges once every thirteen years millions of them at once. It's a defense mechanism the sheer number overwhelms predators. The Cicada does this also to avoid appearing when another species of Cicada appears to prevent cross breeding.
The other species in the same region emerges every 7 years. The two will only emerge at the same time every 220 years (I think it as).
Smart bugs!