Tuesday, July 1, 2014

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Backyard Bugs: Cicadas

The next bug in our Backyard Bug series is the cicada!

What is that buzzing sound?  Oh!  It's a cicada!  

Every summer we notice the cicadas start "singing" about the beginning of June.  And while I know some people who find the sound obnoxious, I look forward to it...almost as much as I look forward to not having to wear a jacket!  

Cicadas are large (often 1" to 2" long) insects with wings that have very clear veins in them.  They have two easy-to-see eyes and three very small "ocelli."  There are about 2500 species of cicadas, and they are very common in warm tropical and subtropical areas. 

Ocelli: small eyes

Cicadas are often heard before they are seen: during the hottest part of the day they make a loud clicking sound by vibrating part of their abdomen like a drum...over and over very quickly!  They have been recorded "buzzing" at over 120 decibels!  And even though both males and females have the same structures, only the males have been recorded buzzing.

An adult female cicada will lay her eggs on a branch or stem that she splits open to make room for the eggs.  When the eggs hatch, the nymphs will drop to the ground and dig a tunnel where they will live for several months as they grow and molt.  Their underground homes are usually between one and eight feet deep.  While they live underground, they will eat sap from tree roots.

When the cicada is ready for its final molt, it will dig its way to the surface and find a branch or fence to hold on to while it climbs out of its exuvia, or old exoskeleton.

This series of photos by Jim Dewitt show the process of the cicada climbing out of its shell wonderfully!

Most cicadas complete the above life cycle in two to five years.  One bizarre exception is the genus Magicicada. These cicadas life cycles take 13 or 17 years!  Most of that time is spent underground as a nymph.  The final adult stage only lasts about two months!

Cicadas are eaten by birds, squirrels, and cicada-killer wasps.

If you find a cicada, it is probably safe to hold. They rarely bite, and probably will only do so after it has rested on a person and mistaken the person for a tree branch.  The bite may hurt, but is otherwise generally usually harmless.  The cicada exuvia are definitely safe to hold!

With Your Preschooler:

Catch a cicada and observe it in a bug observation container.  Can you see the ocelli?  Do you find the veins in its wings?  Each large vein has both a nerve and a trachea.  Why do you think this is?  (So the cicada can feel things touching the wing and get oxygen to the wing muscles.)  Remember to release your cicada when you're done observing it.

Find a cicada exuvia and examine it.  Remember it is from the cicada nymph right before the adult emerged.  How many body features can you find?  How many legs does an insect have?  Exuvia provide an excellent opportunity for dissection, as they are discarded from the insect but still have interesting features!

Some insects, like crickets, can make a sound by rubbing their legs together.  The cicada, however, makes its noise by expanding and contracting muscles in its abdomen...like beating a drum.  Make your own drum using an empty oatmeal canister!  

This post is part of the Backyard Bugs series!  Check out past bugs here and be sure to join us next week when we learn about fire ants!!

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