Discussion: One sure sign we are moving into the hottest days of the summer is the loud buzzing sound of cicadas. It seems the hotter it gets, the louder they sing. It gets to the point where it’s hard to hear your friend talking while you share an iced tea on the porch. For some, it’s a loud nuisance and for others it’s one of those comforting outdoor sounds. However, to scientists, the loud cicada song means so much more.
There are many reasons why cicadas sing. The main reason is to attract a female for mating and to induce reproduction of their species. There are over 2,500 different species of cicada with each having its own distinctive mating song. The two most common cicadas are the Annual Cicada and the Periodical Cicada. Annual cicadas hatch as larva and burrow underground for two to five years. They then emerge from the ground as nymphs when their life cycle nears adulthood. Cicadas, in the second part of their life stage, are called nymphs. Nymphs have a hard shell or exoskeleton that protect them when underground. Once they emerge from the ground, they shed that skin (like a butterfly exiting a cocoon) and climb up the nearest tree. Periodical cicadas are famous for their long lifespan. About every 13 to 17 years, the nymphs reach their adult stage, emerging from the ground in large quantities called “broods”. Whether it be Annual Cicadas or Periodical Cicadas, when soil temperatures in the summer reach above 64 degrees Fahrenheit eight inches deep, they emerge from the ground, climb up the nearest tree, shed their exoskeleton, and make an exceptionally loud chorus. Along with many different types of cicadas and their many different songs, their song increases in volume for only one reason, temperature.
Cicadas are active throughout the day, however, make the most noise during the hours of the afternoon. This is often the average time when the diurnal temperature range reaches its maximum. During this time of day, a cicada’s song can reach up to 105 to 120 decibels which is about as loud as a chain saw. A cicada’s song varies in pitch and frequency due to different temperature cues. Richard Alexander and Thomas Moore of Ohio State University observed that periodical cicadas sang quieter or hardly at all on cloudy, cooler days compared to hot and sunny days. These examples are indicators that cicadas are highly temperature dependent when it comes to their song. The reason for this is within their biology.
Cicadas love it when it gets hot, because it often indicates the courting of a female. Within the cicada’s abdomen there is a muscular membrane in which they vibrate rapidly. This membrane is used to create their loud chorusing throughout the day. A study done by Jerome Sueur and Allen Sanborn showed that when cicadas sing, the vibration of the muscles creates friction and heat within their bodies. This heat creates tension in the muscles which then increases the intensity of their sound, much like tightening a guitar string. With friction creating heat in the cicada’s body, they have the ability to create a body temperature that exceeds that of the air temperature. When the air is hotter outside it helps the male cicadas to increase their sound and make themselves more audible to female cicadas.
According to scientists, cicadas are very temperature dependent because it plays a large role in the cicadas song. They love the heat and the hotter it gets the louder they get. So, when you are trying to have a conversation on the porch over iced tea and you hear the cicadas singing their little hearts out, it would be fun to mention to your friend what you learned in this article.
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© Meteorologist Alexandria Maynard