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?
如果你住在美国东海岸, 那过去的17年里, 你走路、 吃饭、 睡觉, 都在一支休眠的昆虫大军之上。 这些昆虫是蝉。 每17年, 数十亿计的蝉从地下涌出 来做三件事: 蜕壳, 交配, 以及死亡。 共有15窝不同的蝉, 根据它们的出现时间来区分。 有些蝉窝的周期是13年, 而另一些是17年。 不管是哪一种,蝉的生命的大部分时间 都生活在地下, 依靠植物根的汁液存活。 等到要出现的时候, 成虫会开始挖掘 离开地下的通道, 直到地面, 在那里它们将生活仅仅数周。 但是,在这几周里, 所有人都会意识到蝉来了。 它们有数十亿, 而且他们很吵。 雄性蝉集结在一起, 来呼唤雌性配偶, 他们的合唱 可以高达100分贝, 就像电锯的声音。 事实上,如果你正在使用电锯 或是割草机, 雄性蝉会向你集结而来, 以为你是它们的一份子。 和自然界的大部分东西一样, 蝉的到来也不孤单。 随着这些吵闹的虫子一起到来的, 还有各种可怕而又恶心的捕食者和寄生虫。 以团孢霉属的真菌为例。 这些白色的真菌将自身藏匿在蝉的腹中, 侵蚀蝉, 并留下孢子。 当这些孢子破裂时, 它们会从依然活着的蝉的体内爆出, 把虫子变为一个播撒死亡的飞行盐罐, 将孢子洒向 临近的毫无戒备的蝉。 虽然我们精确地知晓 蝉何时会出现和消失, 我们仍然不完全了解其原因。 当然,让整个种群一下子出现 是有一定好处的。 从地下涌出的蝉的数量如此之多, 对捕食者而言是压倒性的。 这本质上保证了 总有一些虫子可以存活并繁衍。 由于蝉每13年或17年才出现, 这比很多捕食者的寿命都要长, 吃它们的动物 学着不去依赖它们的生存 但是,为什么是13年或17年? 为什么不是16年? 或是18年? 或是12年? 这个没人真的知道。 有可能这些数字只是巧合, 或可能蝉真的很喜欢质数。 最终,蝉会交配并慢慢死去, 它们的声音会渐渐弱下去。 它们所产的卵会开始新的周期, 蝉的幼虫会进入底下, 以树汁为食, 等待它们的时候的到来, 来遮盖天际, 将它们的歌声弥漫各处。 17年后它们会准备好。 你呢?