One genus, the periodical cicadas spend most of their lives as underground nymphs, emerging only after 13 or 17 years. The unusual duration and timing of their emergence may reduce the number of cicadas lost to predation, both by making them a less reliably available prey (so that any predator who evolved to depend on cicadas for sustenance might starve waiting for their emergence), and by emerging in such huge numbers that they will satiate any remaining predators before losing enough of their number to threaten their survival as a species.