VOA科学技术2024--US Prepares for a Cicada Invasion Last Seen in 1803（在线收听）

US Prepares for a Cicada Invasion Last Seen in 1803

　　Do you remember all those cicada videos from the United States in 2021?

　　Well, prepare for a repeat performance this year. The insect show begins as early as April.

　　Two groups of cicadas, brood XIII and brood XIX, are expected to come out from the ground to mate and lay eggs this year. Their appearance in the same year is rare. The last time it happened was 1803.

　　Brood XIII is on a 17-year cycle. They will be found in the Midwestern states of Illinois, Iowa, Wisconsin and Kentucky. Brood XIX is on a 13-year cycle. They will come out in an area stretching from Indiana and Illinois southeast to the southern states of Alabama and Georgia.

　　Scientists expect more than one trillion cicadas to appear in some small areas where the two broods are close to each other. The insects will begin to climb out of the ground when the soil warms to about 18 degrees Celsius. So they will be seen in warmer southern areas as early as April. It will be closer to summer, sometime in June, before the cicadas arise to the north in Wisconsin, Indiana and other Midwestern states.

　　Cicadas are large, noisy insects, from about 2.5 to 5 centimeters long. Like most insects, they have wings. They also have big "bulging" eyes. There are thousands of species of cicada around the world.

　　The huge majority of cicada species arise each year, or annually. Then there are the periodicals which arrive after numerous years in the ground.

　　The periodical cicadas emerge to mate.

　　The male cicadas make a thrumming sound with their wings on their bodies to call for mating. The "singing" appeals to females. The insects mate and leave their fertilized eggs on trees. The resulting young fall to the ground after breaking out of their shells. They dig down into the ground where they live for years, feeding on the liquid that comes from tree roots.

　　Seven of the nine known periodical cicadas live in North America. Of the other two groups, one is in India and one is found only on the island country of Fiji.

　　Floyd Shockley is an insect scientist, or entomologist, with the Smithsonian Institution's National Museum of Natural History in Washington, D.C. He said this year's group of cicadas will include four different Magicada species within the XIX brood.

　　The next time brood XIX and brood XIII will come out in the same year will be in 2245.

　　Words in This Story

　　brood –n. a group of young (in this case insects) all born at the same time

　　thrum –v. to make a low, steady sound

　　species –n. a group of animals or plants that are similar and can produce young animals or plants