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Sunday, August 11, 2013

Cicada Cycles

A Cactus Dodger cicada found in Big Bend National Park, TX

A sure sign that we are in the midst of a hot summer is the sound of cicadas buzzing in the air.  For their size, cicadas make as much noise as a large animal, and can be heard up to a quarter of a mile away.  In fact, the word ‘cicada’ is a direct derivation from the Latin meaning ‘buzzer.’ 

Most species of cicadas in North America are in the genus Tibicen, and are generally called the annual or ‘dog-day’ cicadas because they emerge every year in July and August, the dog days of summer.  More widely known are the periodical cicadas from the genus Magicicada, who have a very long lifecycle of 13 to 17 years, and when they emerge, do so in great numbers.     

Tibicen resh, cicada found in Austin, TX
Male cicadas have structures called ‘timbals’ on the sides of their abdomens, and it is with these structures that they create their buzzy songs.  Unlike grasshoppers or crickets that rub their wings or legs together to produce sound, cicadas vibrate these timbals against their hollow abdomens which amplifies the resonance of the sounds.  They can even modulate the sounds by wiggling their abdomens toward or away from the tree trunk on which they are perched.  Each species has its own distinctive sound, and they use different mating songs to attract the appropriate mate.

The lifecycle of a cicada is quite fascinating.  After mating, females deposit hundreds of eggs in a slit made in the bark of a twig, normally on an oak tree.  When the eggs hatch, the nymphs drop to the ground and burrow from 1 to 8 feet, feeding on the juices of the tree roots.  These nymphs spend most of their lives underground, from 2 up to 17 years, depending on the species.  The nymphs then construct an exit tunnel to return to the surface in mid-summer, molt or shed their skin on the bark of the tree, and emerge as adults.  These adult insects are usually 1-2 inches long, have prominent, wide-set eyes, short antennae, and transparent, membranous front wings.   

Empty shell of newly emerged Tibicen resh cicada

While there are over 40 species of cicadas in Texas, the late summer afternoon air in Austin vibrates with the sounds of several annual cicada species such as Tibicen resh (which has no common name) and the Superb Green Cicada (Tibicen superba).  Once every 13 years, the periodical cicadas Magicicada septendecula (which also have no common name) emerges but they are becoming increasingly scarce.  

Cicadas go by a number of common names: locusts (which is technically not correct as cicadas are unrelated to true locusts which are part of the grasshopper family), jar flies (for the way they vibrate or ‘jar’ when held in the hand), June bugs or July flies (in the southeastern US), heat bugs (in Canada and the mid-West), and dry flies (in parts of the southern Appalachian mountains for the shell they leave behind).  Whatever you call them, you’ll be sure to hear and see them in the heat of a Central Texas summer!