Cicadas are flying, plant-eating insects. Most cicada species have life cycles that span 2 to 8 years. They spend most of their lives underground before emerging as adults. In a few species, almost all the individuals in a given location come out of hiding at the same time. These are known as periodical cicadas, and they generally belong to the genus Magicicada.
Periodical cicadas usually have 13- or 17-year life cycles. Their development is so synchronized that practically no adults are present in the 12 or 16 years between emergences. When these cicadas do come out of their underground homes, they appear in huge numbers and create a cacophonous, throbbing din during their brief period of mating frenzy in the open air.