Tuesday, May 31, 2011

The Science of Cicadas

My garden is full of holes and my yard is full of cicadas. This is my first cicada season – they can’t survive the Maine winters, where I used to live. To find out more about them, I did a little research into the science of cicadas.

You can learn a lot from the website of the University of Illinois Extension Service (web.extension.illinois.edu/cicadas). The Extension scientists correctly predicted that the brood of 13-year cicadas which periodically visits Morgan County would appear in late May. There are three different species of these periodic cicadas, and the males have different mating songs, so they will not attract females of the wrong species. Some cicada experts also consider the 13-year and the 17-year cicadas to be different species, but others disagree.

More science can be found at Cicada Central. Well before they emerge, the nymphs complete their exit tunnels to the surface. Then they wait for the soil temperature to reach 64 degrees. On this website, you can hear their wide song repertoire, sung at different stages of mating. The females lay eggs in slits they make in tree branches. After the eggs hatch, the nymphs fall to the ground and burrow down to a tree root, whose juices they will suck before they return in 2024.

Because I work on a college campus, it was easy to find a couple of biologists to tell me more. One suggested to my surprise that cicadas were “tasty”, an opinion that is confirmed by the Extension Service. Insects are mostly protein. In some desert regions, people fry cicadas up and consider them a delicacy. Those people are not playing “Survivor” games. Where food is scarce, any local source of nutrition is valuable.

One of my biologist friends speculated about the origin of the 13- and 17-year cycles. She thought cicadas might have developed these prime number rhythms as an evolutionary defense against predatory animals who appear in shorter regular cycles, like every 2 or 3 years. Cicada populations who appeared on the same cycles would always be devastated by these predators, but a 13-year cycle insures that they will not always overlap. But the other biologist said that certain birds might have adapted to the cicada’s peculiar cycles by having slightly larger clutches, numbers of eggs, in those years when the cicadas offer such a rich food source. A wonder of evolutionary genetics and adaptive behavior.

I asked why the cicadas shed their skins. Surviving underground for over a decade requires a good protective shell against water, worms, rocks, and other dangers. The empty shells are perfect replicas of the cicada’s whole body, including their eyes. After they emerge from the ground, they shed those hard skins all at once. At that moment, they are soft and vulnerable, but soon their outside surface hardens, their wings dry and they fly up into the trees to start the next long cycle. Their life-affirming mission complete, the adults die.

The science of cicadas is like other kinds of science. Some parts are thoroughly understood, while other ideas are less certain. Because the cicadas appear so infrequently, they are much harder to study. When there is uncertainty, there is scientific disagreement, which then gradually diminishes as scientists gather evidence and think about what it means in relation to what they already know.

Except for a few biologists, nobody cares about whether there are 3 or 6 cicada species. Cicadas are inconvenient, but not dangerous in any way. So we accept science for what it is, an ever more precise understanding of our world, which will always have gaps and uncertainties.

But when the subject is important to our daily lives, science becomes political. In politics, unlike science, inconvenient truths are routinely ignored or denied. The very inconvenient fact that the earth’s surface is getting warmer, attested by every government and every scientific organization, is so politically inconvenient that Republican presidential candidates who previously argued that steps should be taken to reduce warming, are now disavowing their earlier statements.

The stakes are very high. Many scientists believe that the kind of storms that have devastated the Midwest this year will be come more frequent this century as the average temperature rises just parts of a degree. That is inconvenient. Even if that piece of uncertain science turns out not to be true, just dealing with a warming climate will take major social investments over many years. Or we can listen to the conservative politicians, the discredited websites, and the paid shills who say, “Do nothing!”

Steve Hochstadt

Jacksonville IL

Published in the Jacksonville Journal-Courier, May 31, 2011

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