May 12, 2011 -- They're noisy. And can be a nuisance. But for the most part they are harmless. Thankfully, they only come out every 13 or 17 years.
The dreaded cicadas have emerged in middle Tennessee this week. Brood XIX to be exact.
This particular brood is of the 13-year variety, as are most of the cicadas in the South. Around cities like Nashville, the cicadas are being spotted emerging from their eggs, clinging to trees and flying around. And soon the air will be filled with an almost deafening, high-pitched shrill as the males sound their mating call.
"It's not something to fear, it's actually an exciting thing to see," said Dr. Frank Hale, an entomologist with the University of Tennessee agricultural extension service.
Hale has been studying insects for more than 30 years. He sees this emergence as a teaching opportunity, because there are a few misconceptions about cicadas.
So here are 13 things, give or take about a dozen, that you never knew about these noisy visitors.
First, they are not locusts. They are a completely different species. Locusts are more akin to grasshoppers.
They do not bite or sting. And they are not attracted to humans, despite the fact that they may fly into you as they are buzzing around.
There are two different cicada cycles; a 13-year cycle and a 17-year cycle. Cicadas of the latter variety are generally found in the northern United States.
While they arrive every 13 or 17 years, that doesn't mean they won't be seen in a particular state again before then. (They made news in the Midwest in 2007.) That's because within the species there are different broods, each with a different timeline. Hence, the next emergence of cicadas in Tennessee, Brood XXIII, will happen in 2015. That brood will mostly be isolated to the western part of the state.
Cicadas usually arrive in early May, after surviving underground by feeding on tree roots. They emerge from the ground when the soil temperature where they live reaches 67 degrees. Four or five days later, the males begin their "chorus" and mating begins.
The females then begin laying eggs in the limbs of smaller trees, as many as 400 to 600 eggs at a time. After six to seven weeks the eggs hatch and the "nymphs," as they are called, drop to the ground and burrow into the soil where they remain for 13 to 17 years.
It is the laying of eggs that poses a danger to small flowering and fruit trees. A female can make five to 20 slits in one branch to deposit her eggs. That causes the branch eventually to wilt and die.
Cicadas: Protect Trees With Cheesecloth
But there is a way to protect these trees. Hale recommends wrapping small trees in an airy cloth, like cheesecloth, and securing it around the trunk. This should be done when the first cicadas are emerging, and left on until they are gone. If a tree is not protected and is damaged, Hale suggests pruning only the dead branches, leaving as many branches on the tree as possible.
The time from emergence to death is approximately four to five weeks. After that the cicadas die en masse. It's not uncommon to find hundreds of dead cicadas piled up under trees in early June.
When they die and decompose, the nitrogen in their bodies fertilizes the soil. "So in a way, it's sort of a plus for the forests to have them because they get a fertilization they wouldn't otherwise get," said Hale.