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Periodic Cicadas: What’s the Big Buzz About?

periodic cicada blog header photo

Cicadas Noise

Have you ever heard the buzz of cicadas?  If you have, you probably remember their distinctive sound!  These insects make a loud buzzing sound that grows louder and louder.  To hear their sound and learn how they make it listen to this video from 1:50 to 2:30!

 

Types of Cicadas

     Annual Cicadas

to show people what an annual cicada looks like
Annual singing cicada clinging to a corn stalk.

There are over 2,500 species of cicadas.  Each species makes its own distinct sound.  Most cicadas are annuals, meaning they return every year.  Annual cicadas are found throughout the United States and in many other parts of the world.  These insects are dark in color with green markings.  They emerge from the ground in the late spring.  Their sound is most often heard coming from trees in the late afternoon throughout the summer.

     Periodic Cicadas

to show people what a periodic cicada looks like
17 Year Cicada perched on a stick with a green background

Periodic cicadas are different.  They only appear every 13 or 17 years!  These insects are only found in the United States.  Groups of periodic cicadas that emerge on the same cycle are called a brood.  There are 30 different broods, and each has been assigned a number.  Broods I – XVII (Roman numerals for 1-17) emerge on a 17-year cycle and live in the Northeast. Broods XVIII – XXX (18 – 30) are on a 13-year cycle and live mainly in the Southeast.  2021 will see the return of Brood X!  This brood is also known as the Great Eastern Brood, and last arrived in 2004.  Unlike the annual cicadas, the periodic cicadas come out in vast numbers.

Periodic Cicadas Life Cycle

     Cicada Nymphs

to show people nymphs emerging
nymphs emerging from the ground

Brood X will emerge In late May or early June.  Once the soil reaches about 64°F at least 8 inches below ground, the nymphs dig their way to the surface.  All of the members of the brood get to the surface within a week of each other.  Up to a million and a half cicadas can emerge per acre.  They cannot sting or bite, so arriving in huge numbers ensures that their species will survive.  They have many predators.  Many amphibians, birds, reptiles, mammals, and even fish feed on them.  They eat until they are too full to eat any more.  The remaining nymphs have a chance of living to adulthood so that they can reproduce.  As soon as the nymphs appear, they try to climb onto the nearest vegetation, from which they suck fluids.  Here, they molt for the last time. 

a seventeen-year cicada on its shell that it molted out of

     Cicada as Adults

When they emerge from their exoskeleton, they are soft and white.  Their wings are wet, and they can not fly.  This is when they are in danger of being eaten by predators.

Adult periodic cicadas are black, orange, and red.  They have one purpose; to reproduce.  They have about six weeks to mate and lay eggs.  After that, they die.  Cicadas have a membrane on their abdomens called a tymbal.  Males contract this muscle, and when they release it, it makes a click, click, buzz sound.  This sound is amplified by the male’s abdomen, which is fairly hollow.  The sound can reach 80 to 85 decibels.  That is about as loud as a vacuum cleaner!  This sound can travel up to a mile.  Females use the tymbal like an ear for detecting the sound of the male.  When a group of males gets together to find mates, it is called a chorus.  A chorus can make a deafening sound!  This noise also helps to keep birds away.

     Cicada Eggs

Once they have mated, the females lay their eggs.  They cut slits along twigs, depositing about 24 to 28 eggs in one slit.  Each female lays several hundred eggs.  It takes about six weeks for the eggs to hatch. 

     Cicada Nymphs Again

The tiny nymphs fall to the ground and burrow into the soil.  They feed on tree roots, specifically, the xylem, which carries water, minerals, and other nutrients up the tree.  They molt four times while under the ground.  Each time they grow a little bigger and dig a little deeper into the ground.  The nymphs stay underground for thirteen or seventeen years!  Periodic cicadas have the longest life cycle of any insect.

Other Interesting Facts

Some people are concerned when they hear the sound of cicadas or see them in such huge numbers.  The truth is, they are harmless to humans.  They may damage small saplings because of the number of eggs that they lay on the twigs.  This does not usually damage mature trees.

According to an article written in Smithsonian Magazine (June 3, 2020),  adult cicadas’ wings are covered in a “natural engineering Marvel: minuscule nanopillars that repel water, kill bacteria, and self-clean”.  Some scientists have tried to design nanopillars as self-cleaning surfaces for solar panels.  

That’s why all the buzz about the amazing cicada!

If you would like to have your students do some reading about cicadas, click the links below.  Resources are available at the elementary and upper levels in Pdf form and for use with Google Slides™.  The elementary resources have a simple STEAM activity, in which students are asked to create a device that muffles sound.  Of course, older students could do the same.

     

If you’re interested in learning more about using science reading passages, be sure to check out our post,  Outstanding Science Reading Passages that Will Engage Students. 

And remember, it’s all science!

Sarah

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