A plague of locusts: here comes Brood X.

• Author: Clay, Keith
• Position: Ecology - Cicadas

"... When periodical cicadas emerge, they do so in enormous numbers--up to 1,500,000 individual insects per acre, weighing over one ton cumulatively. That translates into 1,000,000,000 cicadas per square mile...."

FOR THE LAST 17 years they have been living underground, waiting for their moment in the sun. The wait is practically over. Trillions of periodical cicadas known as "Brood X" are about to emerge from their subterranean homes in one of the largest and most dramatic insect outbreaks on Earth.

Later this month, from New York to Virginia and as far west as Indiana, Illinois, and Missouri, the incessant droning of cicadas will begin to fill the air. Then, after three or four weeks, Brood X will be gone, not to return until 2021. While many broods of periodical cicadas exist, each with its own particular geography and schedule, Brood X, making its first appearance since 1987, is the largest--and loudest--of all.

People familiar with periodical cicadas often call them locusts, even though that name is not correct in a biological sense. This usage probably originated early in American history. Settlers confronted with the sudden appearance of huge numbers of unfamiliar insects may have thought they were seeing a Biblical plague of locusts. However, locusts actually are a type of grasshopper, whereas cicadas are more closely related to tiny aphids, leafhoppers, and spittlebugs.

Periodical cicadas' long life span and their highly predictable emergences every, 17 years--although there also are 13 year periodical cicadas--make them unique among insects. Moreover, except for the eastern portions and midwestern sections of the U.S., these cicadas are found nowhere else in the world. While there are many theories about why cicadas have such an unusual life cycle, scientists do not know for sure. What we do know is that when periodical cicadas emerge, they do so in enormous numbers--up to 1,500,000 individual insects per acre, weighing over one ton cumulatively. That translates into 1,000,000,000 cicadas per square mile, or 38 trillion in the state of Indiana alone. Their dramatic appearance, tremendous abundance, and deafening roar all pique onlookers' fascination.

What can we expect during the next few weeks, and is there anything to worry, about? Thus far, these insects have spent their entire lives below ground, sucking sap from the roots of trees and shrubs. Slowly, each cicada grows to the size of a small shrimp. When soil temperatures...