美国多个地区知了成群

The cicadas are back.

Over the past few weeks, across a wide swath of the eastern United States, the notoriously noisy bugs have emerged by the billions from their long, underground adolescence.

On a muggy afternoon at the farmers’ market in the St. Louis suburb of Kirkwood, Missouri, the cicada invasion is in full force and local residents have mixed feelings about it.

“I just like holding them and putting them on the trees and stuff,” says Matt Covington, 10, who loves the insects. “They tickle when they crawl on you, it’s fun.”

St. Louis Public Radio

Nineteen-year-old Lauren Pierce takes the opposite view.

“Oh my gosh, they look like little devils, and I don’t like it,” she says.     “I think they’re stinking up my neighborhood. They’re rotting everywhere and they smell bad and they’re really loud in some places, and…it’s kind of a nuisance.”

They are definitely make a lot of noise. The males sing to attract mates. Chris Hartley, an entomologist at the Sophia M. Sachs Butterfly House in Chesterfield, says they make that sound by vibrating an organ on the side of their thorax called a tymbal. They actually use their wings to amplify and resonate the sound out, which adds to the racket.

But these periodical cicadas have spent the past 13 years not making any noise at all. They’ve been underground, feeding on the juices of tree roots, as small brown juveniles, or nymphs.

St. Louis Public Radio

“The nymphs are these strange kind of alien-looking things that have no wings, very rudimentary legs that are only good for crawling and nothing else, and they kind of have these huge, claw-like front legs,” says Hartley.

When they’re ready to emerge, the nymphs tunnel their way to the soil surface in the middle of the night, leaving visible holes in the ground a little over a centimeter in diameter. They climb up the nearest bush or tree and molt for the last time, littering the foliage with their old brown casings.

When the adult cicadas first emerge in the darkness, they’re soft, pale white, and very vulnerable. It takes a couple of hours for their exoskeleton to darken, and their wings to unfold and dry to a translucent orange-gold.

The red-eyed adults are about three centimeters long and live for three to four weeks.

“A female will lay, throughout her lifespan, about 600 eggs,” says Glenn Frei, who helps care for the live insect collection at the Saint Louis Zoo. He says female cicadas use a sword-like organ, called an ovipositor, to slice into small tree branches and insert their eggs.

Art Chimes

When the ant-sized nymphs hatch six to 10 weeks later, they drop to the ground, dig a burrow, and start the 13-year cycle all over again. The egg-bearing twigs often turn brown, droop, and die. But Frei says cicadas aren’t locusts – they don’t eat leaves or attack crops.

“They’re causing some minor damage, but overall, even with the massive numbers of them, they’re not going to do enough to kill a healthy full grown tree," says Frei. "Young saplings may get enough damage where it could kill them, just because they’re not old enough, but for the most part a healthy, older tree is going to do just fine.”

Frei says the number of adult periodical cicadas has already peaked in the area and he expects them to die off in the next couple of weeks.