A plague of locusts: here comes Brood X.
FOR THE LAST 17 years they have been living underground, waiting for their moment in the sun. The wait is practically over. Trillions of periodical cicadas known as "Brood X" are about to emerge from their subterranean homes in one of the largest and most dramatic insect outbreaks on Earth.
Later this month, from New York to Virginia and as far west as Indiana, Illinois, and Missouri, the incessant droning of cicadas will begin to fill the air. Then, after three or four weeks, Brood X will be gone, not to return until 2021. While many broods of periodical cicadas exist, each with its own particular geography and schedule, Brood X, making its first appearance since 1987, is the largest--and loudest--of all.
People familiar with periodical cicadas often call them locusts, even though that name is not correct in a biological sense. This usage probably originated early in American history. Settlers confronted with the sudden appearance of huge numbers of unfamiliar insects may have thought they were seeing a Biblical plague of locusts. However, locusts actually are a type of grasshopper, whereas cicadas are more closely related to tiny aphids, leafhoppers, and spittlebugs.
Periodical cicadas' long life span and their highly predictable emergences every, 17 years--although there also are 13 year periodical cicadas--make them unique among insects. Moreover, except for the eastern portions and midwestern sections of the U.S., these cicadas are found nowhere else in the world. While there are many theories about why cicadas have such an unusual life cycle, scientists do not know for sure. What we do know is that when periodical cicadas emerge, they do so in enormous numbers--up to 1,500,000 individual insects per acre, weighing over one ton cumulatively. That translates into 1,000,000,000 cicadas per square mile, or 38 trillion in the state of Indiana alone. Their dramatic appearance, tremendous abundance, and deafening roar all pique onlookers' fascination.
What can we expect during the next few weeks, and is there anything to worry, about? Thus far, these insects have spent their entire lives below ground, sucking sap from the roots of trees and shrubs. Slowly, each cicada grows to the size of a small shrimp. When soil temperatures reach about 63[degrees]F, usually in late May, they emerge from their underground chambers. Like newly hatched sea turtles racing for the ocean to avoid being eaten, the just-emancipated cicadas are extremely vulnerable, which may be why they wait until nightfall to make their break.
They crawl as quickly as they can to the nearest tree or other upright object, climb up, and locate a secure grip. They then molt, slipping off their brittle exoskeletons to become full-fledged adults. It takes a few hours for their new bodies to harden and wings to expand in preparation for the final few weeks of their lives. Their overriding goal during that time is to reproduce.
Male cicadas gather together in large trees in sunny locations and sing to attract females. Only male cicadas sing. This was noted by the Greek poet Xenarchus, who wrote of European (nonperiodical) cicadas, "Happy the cicadas' lives, since they all have voiceless wives," and more recently by Ogden Nash, "Girl locusts don't make any noise, but you ought to hear the boys!"
Brood X's singing will be loudest on hot, sunny afternoons. Some people find the music of cicadas a delightful addition to warm summer days, while other people claim that the incessant droning is annoying, even maddening.
After mating, female cicadas lay several hundred eggs. They use a knife-like appendage to cut small slits in young branches and twigs of woody plants and deposit their eggs in these wounds. A large number of slits causes branches to break off or die. A heavily attacked tree can lose most of its small branches and leaves. Saplings can be killed outright or permanently maimed. Fruit trees especially are at risk. Cicadas seem to love apple trees the most. Some orchard growers in the Midwest qualified for Federal disaster aid in 1987 when cicadas wiped out the entire year's bar vest. If you are worried about your trees and shrubs, cover them with netting to prevent females from getting close enough to lay eggs.
After several weeks, the eggs batch and baby cicadas drop to the ground, burrow in, and are not seen again for 17 years. Like salmon returning to their native stream to spawn after many years at sea, cicadas spend almost their entire 17-year life span preparing for a few weeks of singing and mating. Also similar to salmon, there is a no overlap between the end of one periodical cicada generation and the beginning of the next. All adult Brood X cicadas will die before their offspring hatch.
Other than damage to trees, the profusion of cicadas poses little harm to humans. Cicadas may cause alarm when they fly onto your shirt-sleeve, but they do not carry diseases, bite, or sting (except by accident).
Many people welcome the reappearance of periodical cicadas. For example, certain Native American tribes feast on the plump cicada nymphs as they emerge from the ground. Gene Kritsky, a renowned cicada biologist at the College of Mount St. Joseph in Cincinnati, Ohio, says the cicadas taste like canned asparagus. A few dozen stir-fried and served over rice make for a tasty treat.
Many people may have noticed that their yards are being churned by moles to an alarming extent. Mole populations are at an all-time high in many suburban areas where Brood X cicadas are abundant in the soil. With so many cicadas to cat, moles can raise larger families. But rest assured, the mole problem soon will solve itself. After Brood X emerges, mole populations will plummet. As far as moles are concerned, the new generation of cicadas simply are too small to eat and will not reach an edible size for at least 10 years.
The impending emergence may reflect a survival strategy that biologists call "predator satiation." There are so many cicadas that there are not enough predators to eat them all, thus leaving some adults (and their offspring) alive to reproduce again. It is not that predators do not try to devour them. Pretty much all of the local wildlife will drop what they are doing for a few weeks and gorge themselves on cicadas--even domestic animals such as cats and dogs.
With the aid of National Science Foundation grants, a group of Indiana University scientists hopes to determine whether cicadas have a significant impact on forests. The cicadas' enormous population sizes and their long-term parasitism on tree roots suggest that these curious creatures indeed might affect the way forests grow and change. The lower Midwest and southern Indiana in particular are at the epicenter of the Brood X emergence. Of course, there will be astonishing numbers of cicadas over a much larger region as well. Eastern forests are being threatened by a growing list of invading insect pests like the gypsy moth, emerald ash borer, and hemlock woolly adelgid. Could cicadas have an equally large, but more subtle, effect on forests?
A major goal of our research is to see what happens when Brood X cicadas' life cycle is disrupted by covering large swaths of young forest with netting, which will keep them at bay during the crucial period in which females normally would lay their eggs. We will compare netted, cicada-free areas with uncovered sections. This essentially is the start of a 17-year experiment, but we hope to have some results before 2021.
Although humans dominate the world in so many ways, some things are out of our control. A biological event of the magnitude of Brood X emphasizes that fact. We should be happy that cicadas are not killer bees or blood-sucking ticks. They simply are a benign (hopefully) part of nature--so sit back and enjoy the show.
Keith Clay is professor of biology, Indiana University, Bloomington, and director of the Research and Teaching Preserve system.
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|Title Annotation:||Ecology; cicadas|
|Publication:||USA Today (Magazine)|
|Date:||May 1, 2004|
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|Observations on periodical cicadas (Brood X) in Indiana and Ohio in 2004 (Hemiptera: Cicadidae: Magicicada spp.).|
|Food habits of mammals during an emergence of 17-year cicadas.|