Tuesday, May 31, 2011

Attack of the Teenage Cicadas

On May 20, my father-in-law sent me an email with the subject line: They're here!!! Attached were two photos of adult cicadas who had shed their nymph-stage skin to climb into the trees to mate. These cicadas (Magicicada sp.) were part of the Great Southern Brood (Brood XIX) that emerges every 13 years in parts of southern Illinois as well as much of the southeastern United States.

I wasn't confident that we'd see an emergence as far north as Champaign, so I was excited when my father-in-law reported the Brood XIX cicadas had crawled up from the soil around Lake Sara in Effingham. When we arrived for a family holiday this past weekend, the first thing we noticed was the constant drone of the cicadas in the towering oaks. Much lower in tone and less modulating than the annual cicada, the singing of the Brood XIX cicadas is almost pleasant to experience. Throughout the weekend, we tried to discover a fitting description for their song. Some thought it sounded like the song of frogs; others found it reminiscent of water running through a narrow pipe. At times, it sounded like low-budget sound effects from a B-rate monster movie.

During both days we were at the lake, I took time to walk through the woods and along the shore to photograph these amazing creatures.














After spending a couple of days marveling at these insects, whose appearance is simultaneously magestic and alien, I keep coming back to the unusual nature of their life cycle. I wonder what evolutionary advantage is provided by feeding below the surface for so long, only to emerge as teenagers for a few short weeks of mating and egg laying. Come to think of it, maybe it's not all that different than Spring Break in Daytona Beach.

For more information on the 13- and 17-year cicadas, please visit this Illinois Natural History Survey website.

5 comments:

  1. I find cicadas pretty fascinating, too. You got some really great photos, Chris! Even molting!

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  2. Thanks, Kylee. There were so many great photo ops, in all stages. Just fascinating.

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  3. I took nearly 400 photos, kept about 45 of the best ones.

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  4. As I understand it, the probable evolutionary advantage to the extremely long generations is overwhelming their predators. All those cicadas flying around are a bonanza for birds and everything else, but with SO many of them, their predators can't begin eat them all. But the predator population can't increase to take full advantage of all that food, because then they'd starve the other 12 years. Many trees have a similar strategy when they have "mast years." For example, all the oaks in an area produce huge amounts of acorns one year, and tiny amounts other years, overwhelming the ability of squirrels etc to eat them all. How the different trees in an area get in sync for mast years is still a mystery.
    Also another cool bit of trivia: All the periodic cicadas have life cycles in years that are large prime numbers -- 13 and 17. That way, when populations of different sorts of cicadas overlap, they only ever emerge and breed the same year every 221 years! This virtually eliminating the chance that they'll have problems with accidentally interbreeding with the other cicada type.

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  5. Thanks, Joseph. That makes good evolutionary sense, although I'm having a bit more difficulty imagining the selection scenario that resulted in the exact number of years. Perhaps over a very long period, the prime number cycle had some advantage as well.

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