From late May through June, Brood X of the periodical cicadas will emerge from the ground, having spent the past 17 years as nymphs feeding off tree roots. After digging their way out and molting into adults, billions of the big, clumsy, red-eyed insects will sing their earsplitting love songs. Last seen in 1987, the brood will provide a prodigious if brief feast for birds, along with an incomparable opportunity for researchers. Fascinated naturalists have been writing about periodical cicadas for four centuries. But much remains unknown about the insects' periods or what triggers their synchronized appearances.
Brood X is perhaps the largest and best studied of the approximately 15 broods of periodical cicadas (researchers dispute the exact number). A brood emerges somewhere east of the Great Plains almost every spring. Worldwide, investigators have identified some 3,000 cicada species but know the life cycle for only a dozen or so. William Bradford, governor of the Plymouth Colony, first described periodical cicadas in 1633, although Native Americans probably knew of the creatures before then. The 17-year life cycle was firmly established less than a century later; by the mid-19th century, naturalists had recognized 13-year cicadas.