The Bursts of Cicadas Every 17 Years Punctuate Our Human Existence
by Sylvan Bachhuber, age 14
At 17 years of age, many of us have barely reached our first rites of passage, let alone our expiration dates. But at 17, the periodical cicada ends its life, making it the longest living insect.
A new generation of cicadas came of age this year in the eastern United States, announcing their arrival with a chorus of ringing clicks, made by the snapping of rigid plates on their abdomens and the clicking of their wings.
The most recent army of periodical cicadas was laid in 1996. They hatched in the trees and developed for a few weeks, before billions of young cicadas rained down to the ground below, where they feasted on fluid from tree roots underground. This year, the 1996 batch emerged to mate. Shortly after reproducing and laying their eggs in trees, they died.
The cicadas’ beautifully synchronized life spans have been choreographed by years and years of evolution through natural selection. Natural selection is the process where the weakest animals in a species die out, leaving only the strongest specimens to carry on the species. When individual cicadas emerge in the wrong year, out of sync with their brood, predatory birds quickly gobble them up. But when billions of cicadas emerge together, they overwhelm their predators. Nature, it seems, favors strength in numbers. Because of their large numbers and simultaneous presentation, cicadas are unstoppable. So effective is this method of synchronization that selection for their less important defenses, such as flying ability, has more or less fallen by the wayside.
Throughout the U.S. there are 15 “broods” or groups cicadas hatched near the same time, on different cycles. Although most broods have 17-year life cycles, a few in the U.S. cycle every 13 years. Cicadas that migrate to a territory inhabited by a different brood can quickly adapt to the cycle of their new home. Those that lack this ability will quickly die. This phenomenon has caused the species to switch between cycles very rapidly. In fact, in the last half million years periodical cicadas have gone back and forth between 13 and 17-year cycles at least eight times.
The 17-year intervals within a cicada’s timeline can remind us of the rites of passage we have crossed. Our society has changed so drastically since the last generation of cicadas hatched. When the next generation arrives, who knows what kind of place our world will be?
[Source: New York Times]