Monday, October 17, 2011

split cicada husk

split cicada husk
clinging to box elder bark --
nymph body long gone

It was my father who first showed me one of the strange brown husks clinging by the thousands all over the bark of our big apple tree. It looked like a dead insect with creepy claws and bulging eyes. He pointed out the slit down the back and claimed that another insect, twice as big, had emerged from inside and after its wings dried it had flown away. My father told a lot of tall tales, like the one about flying catfish, so I didn't really believe the part about a giant bug coming out of that little empty shell. "Listen," he said, and I tuned in to the deafening "wee-ah, wee-ah" permeating the humid summer evening. "That's a chorus of boy locusts singing a love song to their girlfriends." What a strange song, I thought, eerie and hypnotic. Then my father did a scary thing. He plucked the papery corpse off the bark and placed it right on my shirt, where it's little claws clung to the soft fabric. I flinched, but the bug didn't bite or pinch or crawl up my neck, so I got used to walking around with a dead bug on my shirt, like a brown paper pin. After awhile I started collecting them and even wearing them in my hair.
          What my father called 17-year locusts are periodical cicadas that live underground for either 13 or 17 years. The nymphs remain attached to the roots of plants and feed on the sap. During this time they go through five molts. In the late spring of their last juvenile year, they dig tunnels and then emerge in a huge, mass migration, crawling up the plant to molt into winged adults. In the short space of about a month, the males congregate by the thousands, often in one tree, to sing their mating call, the loudest known insect call at up to 100 db. Females fly to the "chorus tree" where they mate and lay eggs. Then they both die. One time I was lucky to witness a red-eyed cicada slowly emerge from its nymph shell. Then it crawled higher up in the pine tree to rest for a few days, waiting for its pale exoskeleton and transparent wings to harden completely and turn dark green.

          Why do periodical cicadas emerge in prime numbered years? Scientists believe this represents an adaptation to the colder soil temperatures during Pleistocene glacial periods. How do they know when to come out from the dark ground after such a long time? Scientists think they take cues from the seasonal signals of the trees as to how many years have passed. Last year, 2010, a weird aberration in their 17-year cycle happened here in southeast Iowa, when a small number of the insects emerged four years ahead of schedule. According to Donald Lewis, professor of entomology at Iowa State University, they appeared in 1963, 1980 and 1997, and they should not have appeared again until 2014. No one knows why. "What has changed so much in our lifetime," Lewis asks, "that the cicadas would change a fundamental part of their lifecycle and make this mistake? Climate change is one possibility."

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