A spectacular wonder of nature or an anxiety-inducing nuisance? It depends on whom you ask. Naturalists have already spotted the first arrivals in a rare phenomenon during which cicadas emerge this spring across more than a dozen U.S. states — including populous areas like Chicago, Nashville and St. Louis — blanketing eastern parts of the country with billions, perhaps trillions, of the flying bugs. The insects will infiltrate a much bigger geographical area than similar occurrences in most years because they’re part of the dual emergence of two particular periodical cicada broods. These groups of multiple Magicicada species appear like clockwork after a certain number of years, but the simultaneous appearance of these two broods hasn’t happened since 1803. The Northern Illinois brood spends 17 years underground before emerging and is known as Brood XIII, while the Great Southern Brood, or Brood XIX, lives underground for 13 years. The two broods won’t coincide again until 2245. When small holes that can resemble tiny chimneys appear in the ground near tree roots, it’s a signal periodical cicadas will soon emerge from their underground lair. Once the soil hits the right temperature, around 17.8 degrees Celsius, cicada babies, called nymphs, begin to burst forth. As soon as they’re above ground, the bugs make a beeline for a vertical surface — typically a tree trunk, but it could be a fence. There they shed their hard outer skeletons and spread their wings for the first time before spending four to six weeks in a noisy frenzy of eating, mating and egg laying. The most obvious sign of their arrival is the distinctive sound they make — a droning buzz. The bugs congregate in trees, and the male cicadas form a cacophonous chorus of thousands to attract mates. “When they say it’s as loud as a lawn mower, it is as loud as a lawn mower,” said Paula Shrewsbury, a professor in the department of entomology at the University of Maryland. “We live near an airport, and when the planes are flying over…cicadas crank up their sound level, it’s like they’re competing with the airplanes for sound,” Shrewsbury said. Female cicadas use an egg-laying organ, called an ovipositor, to lay their eggs inside slits they cut into tree branches. However, cicadas are unlikely to cause any irreparable damage to plants, trees, vegetable patches or flower beds, said John Lill, a professor of biology at the George Washington University. It’s possible that the insects could damage a very young sapling, and to prevent that you could cover the sapling with protective netting, Lill said. Cicadas provide an all-you-can-eat buffet for many animals, including pets. Lill said he once had to take his dog to the vet after it gorged itself on cicadas, but the bugs — which are said to have a sweet, nutlike flavor— are not innately harmful when eaten by pets or humans. However, humans with seafood allergies should avoid eating cicadas, which are distantly related to shrimp and lobsters.(SD-Agencies) Words to Learn 相关词汇 【渗透】 shèntòu infiltrate gradually enter, permeate, or pass through a substance or area 【产卵器】 chǎnluǎnqì ovipositor a specialized organ (as of an insect) for depositing eggs 是自然奇观还是烦人的滋扰?这可见仁见智了。 今年春天,美国十几个州(包括芝加哥、纳什维尔和圣路易斯等人口稠密地区)将涌现一大批蝉;数十亿甚至万亿只虫虫将出现在美国东部地区,自然学家已经注意到了首批“访客”。 与过往大多数年份的类似情况相比,这些昆虫今年渗透的地域范围要大得多,因为两种不同的周期蝉同时出现了。这些蝉每隔一些年出现,像钟表一样准时。自1803年以来,这两种蝉还未同时出现过。 伊利诺斯州北部的周期蝉在地下生活了17 年后再次出现,称为“蝉十三”,而南部的周期蝉“蝉十九”则在地下生活了13年。直到2245年,这两种蝉才会再次同时出现。 树根附近的地面上出现像小烟囱一样的小洞时,周期性蝉就要从地下钻出来了。 一旦土壤达到合适的温度(约17.8摄氏度),称为若虫的蝉的幼虫就会破土而出。离开地面,它们就直奔垂直于地面的歇脚地 —— 通常是树干,也可能是栅栏。 在那里它们褪去硬壳,张开翅膀,然后在接下来的四到六周里疯狂进食、交配、产卵。 宣布它们到来的最明显标志就是虫虫独特的鸣叫。为吸引配偶,成千上万的雄蝉聚在树上,加入聒噪的合唱。 马里兰大学昆虫学系教授宝拉•什鲁斯伯里说:“有人说蝉的叫声像割草机,他们没有夸张。” 她接着说:“我们住在机场附近,飞机飞过时 ...... 蝉还会提高音量,好像生怕自己的大合唱被飞机的轰鸣盖过。” 雌蝉在树枝上划开缝隙,然后把产卵器伸进去产卵。 乔治华盛顿大学生物学教授约翰•利尔说,蝉不太可能严重危害树木、菜地或花坛植物,但可能会损害幼苗。为防止这种情况,他建议给树苗套上保护网。 蝉是许多动物的美食,包括宠物。利尔说,有一次他的狗狗吃了太多蝉,不得不去看兽医。据说蝉有一种甜甜的坚果味;宠物或人吃了它不会有什么危害。不过,对海鲜过敏的人应该避免食用,因为它和虾、龙虾有很远的亲缘关系。 (Translated by Debra) |