If you live on the east coast of the United States, you've spent the last 17 years of your life walking, eating and sleeping above a dormant army of insects. These are the cicadas. Every 17 years, billions of them emerge from the ground to do three things: molt, mate and die. There are 15 different broods of cicadas out there, grouped by when they'll emerge from the ground. Some of these broods are on a 13-year cycle, others are on a 17-year clock. Either way, the cicadas live underground for most of their lives, feeding on the juices of plant roots. When it's time to emerge, the adults begin to burrow their way out of the ground and up to the surface, where they'll live for just a few weeks. During these weeks, though, everybody will know the cicadas have arrived. There will be billions of them. And they're loud. Male cicadas band together to call for female mates, and their collective chorus can reach up to 100 decibels -- as loud as a chain saw. In fact, if you happen to be using a chain saw or a lawn mower, male cicadas will flock to you, thinking that you're one of them. Now, like most things in nature, the cicadas don't arrive without a posse. There are all sort of awesome and gross predators and parasites that come along with the buzzing bugs. Take the fungus Massospora for example. This little white fungus buries itself in the cicada's abdomen and eats the bug alive, leaving behind its spores. When those spores rupture, they burst out of the still-alive cicada, turning the bug into a flying saltshaker of death, raining spores down upon its unsuspecting cicada neighbors. But while we know pretty precisely when the cicadas will arrive and fade away, we're still not totally certain of why. There are certain advantages to having your entire species emerge at once, of course. The sheer number of cicadas coming out of the ground is so overwhelming to predators, it is essentially guaranteed that a few bugs will survive and reproduce. And since cicadas emerge every 13 or 17 years, longer than the lifespan of many of their predators, the animals that eat them don't learn to depend on their availability. But why 13 and 17 years, instead of 16 or 18 or 12? Well, that part no one really knows. It's possible the number just happened by chance, or, perhaps, cicadas really love prime numbers. Eventually, the cicadas will mate and slowly die off, their call fading into the distance. The eggs they lay will begin the cycle again, their cicada babies burrowing into the earth, feeding on plant juice, and waiting for their turn to darken the skies and fill the air with their songs. In 17 years, they'll be ready. Will you?
如果你住在美國東岸 用你過去十七年時間 走路 吃東西 和睡覺 在休眠的昆蟲大軍之上 這些昆蟲就是蟬 每十七年時間 數十億的蟬,從地表出現 來做三件事 脫皮 交配 及死亡 當牠們從地表出現時 被歸類為十五窩不同的蟬 有些蟬窩的週期為十三年 其它則為十七年 不論何種形式,這些蟬大部分時間 都住在地底下 食用植物根部的液體 當該露面的時候 成蟬就開始挖掘 離開地底的通道 直到地面 牠們只會待上幾個禮拜 而這段期間裡 每個人都知道蟬已到來 其數量高達數十億 且聲響驚人 雄蟬會一起行動 邀請雌蟬 牠們集體行動的聲響 可達到近一百分貝 和鏈鋸聲響一般 事實上,如果你恰巧用上了鏈鋸 或割草機 成群公蟬就會飛向你 認為你是牠們其中一員 如同自然定律 牠們不會單獨行動 因為有各種可怕又噁心的 掠食者及寄生蟲 伴隨牠們而來 以寄生菌 massospora 為例 這白色小菌種將自己隱藏 在蟬的下腹中,侵蝕蟬肚 並將種子留下 當這些種子破裂時 牠們從仍活著的蟬腹中噴出 讓蟬的下腹如鹽巴揮灑 斷裂開而死亡 並將種子灑落 在未加思索的隔壁蟬身上 雖然我們清楚的了解 這些蟬會來到繼而死亡 但仍不完全確定為什麼 當然囉!讓整個物種同時出現 有一定的好處 數量龐大的蟬從地下而來 對掠食者而言聲勢浩大 實質上能保證的是 少數蟲子能存活、繁衍下一代 由於蟬每十三或十七年才出現 壽命比起很多牠們的掠食者都要長 捕食蟬的動物都 不會依賴牠們的存在 該想想為何是十三和十七年 而不是十六 十八 或十二年 沒有人真正知道答案 這個數字很有可能只是碰巧發生了 或許蟬很喜愛質數 牠們最後會交配並慢慢死亡 蟬鳴消逝於遠處 牠們下的蛋會再度延續生命 蟬寶寶在地表洞穴裡 以植物汁液為食 等待牠們的時刻 來染黑天際 並賦予美妙的歌聲 牠們用十七年時間準備 你呢?