Displaying items by tag: cicada life stage

Toward the end of their lives, periodical cicadas emerge from the ground, molt into their adult wardrobe to find each other and reproduce before they die. Periodical cicada nymphs spend their entire 13-year or 17-year lives underground seeking nourishment in roots and slowing growing before time to emerge.  Stephen Lyn Bales/Hellbender Press

Billions upon billions of cicadas will emerge this spring and summer during a rare convergence of broods

Three years ago, Southern Appalachia experienced the emergence of 17-year cicadas’ Brood X. And already, we’re up for another wave of cicadas!

KNOXVILLE — Periodical cicadas are rare. Of the roughly 3,400 cicada species on the planet, only seven of those live underground as nymphs for a staggeringly odd long time. 

It gets odder. The seven species are only found in eastern North America, living in 15 separate populations known as “broods.” Some of those broods remain in their subterranean tunnels for 13 years, and some for 17 years. 

When their life cycle is up, the strange little insects emerge by the millions to molt into adults and with their new golden wings fly up into the trees where the females and males find each other. They mate, she lays eggs, and then they drop dead.

When the early American colonists moved to their new homeland in the 1600s they were horrified by these oddly spaced natural phenomena. Pilgrims at Plymouth reported them in 1634. With only a sprinkling of education to serve them, they naturally turned to their only field of reference and the stories from the Bible. The New World newbies deemed them to be swarms of locusts from the list of Biblical Plagues beset on Egypt along with water turning to blood, lice, boils, flies, hailstones and the killing of first borns. And why not?  To them a bug was a bug, with some more frightening than others. 

Here is some evidence of tree browning and “flagging” caused by the recent appearance of Brood-10 cicadas earlier this summer.  Courtesy Oak Ridge National Laboratory 

Tree “flagging” is a lingering sign of the 17-year cicadas’ brief time on Earth

(Alexandra DeMarco is an intern in ORNL’s media relations group.)

On the road leading to the U.S. Department of Energy’s Oak Ridge National Laboratory, drivers may notice that many of the green trees lining the entrance to the lab are dappled with brown leaves. At first glance, the sight isn’t extraordinary, as deciduous tree leaves turn hues of oranges and browns before falling to the ground each autumn.

Yet, just weeks past the summer solstice, this phenomenon is out of place and is in fact evidence of another natural occurrence: cicada “flagging.”

This spring, Brood X cicadas emerged from the ground after 17 years and swarmed across the eastern United States, leaving a trail of exoskeletons and echoes of mating calls. Cicadas emerge in such large quantities to withstand predation and successfully maintain their populations, and trees actually play a key role in their life cycle.

A male cicada attracts a female through a mating call, the sound responsible for cicadas’ shrill hum. After the two mate, the female cicada uses a sharp tubular organ called an ovipositor to slit the bark and split the sapwood of young tree branches to deposit her eggs there. These incisions, however, damage a tree’s vascular system and can cause stalks beyond the incision to die and wither, leaving behind twigs with brown leaves that resemble flags dangling from the trees.

The eggs then grow into nymphs that make their way to below ground. An oft-repeated misconception is that they’ll stay dormant for 17 years. Actually, during that time, they go through 5 life stages while feeding on the xylem (tree sap) of roots. This may further weaken saplings that were heavily infested with cicadas.