Periodical Cicadas: Flying insects of the order Homoptera. While all cicadas have multiple-year life cycles, the varieties that emerge into adulthood all at once are known as periodical cicadas. There are seven species of periodical cicadas in North America, all belonging to the genus Magicicada. Some of these species have 13-year cycles, and others have 17-year cycles. What this means is that each brood spends most of a 13- or 17-year period growing as nymphs in the root systems of their hosts, then emerge en masse as adults to completely overrun their environment.

Like many other insects, adult cicadas are basically breeding machines. All they do during their brief adult lives is gather in crowds, sing a lot and fly around looking for mates. During this time, they feed on plant fluids and make the most alarming racket imaginable.

The dominant theory explaining the brood cycles is that the odd periods allow the cicadas to escape most natural predation. In a single night, millions of cicadas can emerge into tiny areas, and although thousands of them do get eaten, the local predators are usually sated well before they make a dent in the new cicada population.

All cicadas of the same life-cycle emerging in a given year are known collectively as a brood. The North American broods are designated by Roman numerals. Brood XXII emerged in the South in Spring 2001, followed a few months later by Brood VII in New York. Brood XXIII will emerge next year spread throughout the Midwest, followed by Brood VIII in Ohio, Pennsylvania and West Virginia. I like to say this because it sounds nice and ominous, the kind of line the geeky scientist type always says in a disaster movie.