Sweet Seventeen: The Cicadas Return
Air Date: Week of June 21, 1996
The last time this species of cicadas was around, Jimmy Carter was in the White House. The periodic, or 17 year cicadas, are back. Reporter Tom Verde talks with some insect experts on what makes these time sensitive creatures tick. Or chirp.
CURWOOD: The moment in the sun has arrived for a rather peculiar insect. After 17 years living underground as grubs, millions of cicadas are emerging this month in eastern forests and suburbs from North Carolina to Connecticut. They'll spend just a few short weeks above ground. In a loud and buzzing fury they will mate and then die. The next generation will in turn burrow beneath the Earth' surface for another 17 years. Yet, because what may have been a forest years ago might now be a housing development or a strip mall, the 17-year cicada's habitat is disappearing. But as Tom Verde reports, some folks in Connecticut have created a preserve for these unusual insects.
VERDE: The year was 1979, the last time residents of Hamden, Connecticut, heard this sound.
(Loud cicada whirring)
VERDE: That's the unique mating call of the periodical, or 17-year cicada. And it's music to the ears of retired Yale entomologist Charles Remington.
REMINGTON: This is the only cicada preserve in the world. It's called the Maja Cicada Reserve. And it's set aside in perpetuity to conserve these marvelous insects that are so vulnerable to extinction. Of the approximately 75 colonies that we had information on in Connecticut in the earlier days, we're down to about 40, and that's too great a loss.
VERDE: Remington spearheaded the effort to establish the 90-acre reserve just 9 miles north of New Haven. He is one of only a handful of periodical cicada specialists in the country who say the creature's unique life cycle, one of the longest of any insects, is one reason they find the cicada so fascinating. The bugs spend 17 years underground, slowly feeding on tree roots, until practically on cue they all emerge at about the same time.
REMINGTON: A working hypothesis for that is that their secondary brain has a counter in it that says one year, two years, three years, and so on. And when they've counted 17 times, then it's time for these by now big juveniles to come up toward the surface of the soil from 15 inches to 5 feet down where they have spent their 17 years.
VERDE: These juveniles, or nymphs as they're called, attach themselves to foliage, shed their pale yellow skins, and in the matter of a few hours harden into adults. The adult cicada is an inch long black insect with large golden gossamer wings and bulging orange red eyes.
(Loud cicada whirring)
VERDE: Eager to attract a mate, the male cicada begins to sing by vibrating membrane-covered ribs on either side of its abdomen. When hard in unison, this mating song has been compared to the eerie pulse of a flying saucer.
(Combined cicada whirring, with bird song)
VERDE: The females deposit up to 600 fertilized eggs in small grooves, which they cut in the twigs of tree branches. After several weeks, the eggs hatch, and the ant-sized nymphs drop to the forest floor where they burrow into the earth in search of a tree root to suck on, and the whole process starts all over again. There are 13- and 6-year cicadas as well as the so-called dog day cicadas which come out every August. But the 17-year species are found only in the eastern US.
(More cicada whirring)
VERDE: Scientists aren't exactly sure why the 17-year cicada has evolved such a long life cycle. But entomologist Chris Simon of the University of Connecticut at Storrs says there are a couple of popular theories.
SIMON: Presumably there are no predators that can have a life cycle as long as theirs, so it cuts down on the predators that meet them every few generations.
VERDE: Another theory, says Simon, is that at one time there were periodical cicadas that emerged more frequently, but this led to overlapping and interbreeding among the species.
SIMON: Having a prime numbered life cycle cuts down on the number of times that you would meet the other life cycle. And that would cut down on interbreeding, or hybridization, between the species. Because presumably hybrids don't survive as well.
VERDE: Because of their dense populations and their resemblance to migratory locusts, cicadas have often been mistaken for the crop-damaging bugs of Biblical fame. In truth, cicadas do little damage to mature forests, although orchard owners complain that the incisions made in tender branches by egg-laying females can sometimes kill young fruit trees. It has been man and not cicadas who cleared the forests over the past century, reducing the insect's population by more than 50%. Simon says the cicada preserve in Hamden will guarantee that there will always be a population on hand, as she and her colleagues continue to study the DNA of periodical cicadas to learn more about how and why species diverge. Meanwhile, researchers elsewhere are already looking to the Connecticut preserve as a model for similar sanctuaries in their own states. For Living on Earth, I'm Tom Verde.
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