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At the end of summer, during what locals call "dog days," evening time porch talk must be curtailed because it is difficult to hear over the noise which rivals the sounds of a rock concert. The noise you hear is the sound made by mate-seeking insects known as cicadas. Grasshoppers, locusts, and katydids are not the same as these rowdy creatures and certainly do not produce the amplified sound.
There are many stories and rumors about these creatures and for good reason. Their life cycle is complex and was not even discovered until the 1960's about the same time as the historical Woodstock Celebration. Also, since the cicada spends most of its life cycle underground, it is difficult to study the animal. The different species of cicada clouds the picture even further. There are species that hatch yearly, then there are the species that only emerge every 13 to 17 years. The latter are known as the periodic cicadas and are distinguishable from the year-to-year cicadas by the brightness of their eye color. The periodic cicadas have an interesting lifestyle.
What do they do? How do they spend their time? Females lay their eggs in trees by cutting a gash in a twig and filling it with eggs. Once they hatch, the offspring fall to the ground and burrow into the soil. But they do not sleep as some folks will tell you. No, they tunnel through the ground and suck water out of tree roots. They have powerful sucking muscles to say the least. After years of this burrowing and sucking, they finally come to rest for a period of four years. When they have rested, some signal occurs and they emerge from the soil. They eventually wiggle free of their exoskeleton. While underground, they go through several insect stages, ending with the one we see on trees in the fall. This gives us the brown, hardened outer shell that kids love to play with in the summer. They spend 4-6 weeks singing to find mates, breed, then die. All this takes 17 years!
What We Need to Know
A great science teacher by the name of Dr. Kritsky designed a project for his science class. He wanted to follow the life cycle of the periodic cicadas over the seventeen-year period. He had his students read the original paper describing the stages of the cicada, then asked the students to write down what they thought they would find when they dug up the soil in an orchard on campus. He began his exercise in 1991. He monitored the progress of the cicadas with every new class, year to year. The students came to have a little joke about his cicada exercise because they always knew it was coming. . . regardless of what he was teaching!
The students kept making their predictions based on the 17-year cycle and each year they were surprised to discover that the insects were much further along in development and seemed ready to hatch ahead of schedule. Being a good scientist, Kritsky believed in the observations of his students and proposed that somehow the cicadas had skipped their usual 4-year rest cycle and were maturing ahead of schedule. Low and behold, in May of this year, Kritsky discovered that the cicadas he had been following were indeed hatching 4 years early--just as his students had predicted over the years.
What We Need to Know
Choose another insect and draw out its life cycle.
From the discovery made by Dr. Kritsky and his classes over the years, make a one-page statement as to why his way of conducting science labs was a good teaching method.
Milius, Susan. Cicada subtleties: What part of 10,000 cicadas screeching don't you understand? Science News. Vol. 157, pp. 408-410.