Why do bugs swarm over water? - Luke M. Jacobus

翻译人员: Mina Liu 校对人员: Sue Lu

Like so many winged insects,

就像许多有翅膀的昆虫一样，

the world’s roughly 4,000 mayfly species take to the skies

每年全世界大约有 4,000 种蜉蝣

都会飞向天空

for their annual reproductive ritual.

进行繁殖仪式。

These flights happen above every kind of freshwater body on Earth,

这些飞行会出现在 各种淡水水域的上空，

barring Antarctica and a few remote islands.

除了南极和一些偏远的岛屿之外。

But whether the breeding mayflies are large Hexagenia limbata,

无论繁殖的是大型蜉蝣 Hexagenia limbata、

tiny Paracloeodes minutus, or the thousands of species in between,

小型蜉蝣 Paracloeodes minutus、

还是介于两者之间成千上万种的蜉蝣，

their time on the wing will be brief.

它们在空中飞行的时间

Very brief.

非常短暂。

For most mayflies, adulthood lasts roughly one day.

对于大多数的蜉蝣来说，

成虫的寿命大约只有一天。

And for some species, it’s only a matter of minutes.

有些种类

甚至只有几分钟。

This isn’t because they’re all eaten up by predators—

这并不是因为它们都被天敌捕食了——

though they are a favorite food of many fish, birds, and larger insects.

虽然它们是很多鱼类、鸟类 和大昆虫最喜欢的食物。

Rather, this abridged adulthood is a natural part of their life cycle.

这种简短的成虫期，

是它们生命周期的一部分。

A close look at these insects reveals they've ditched functional mouths

仔细观察这些昆虫，

就会发现它们已经失去了

功能性的嘴巴和消化系统。

and digestive systems.

Without these innards taking up space, mayfly bodies can store more eggs,

没有这些内脏来占据空间，

蜉蝣的身体可以储存更多的卵，

with some species producing up to 12,000 per individual.

有些种类每只可产出 多达 12,000 个卵。

This adaptation is essential to mayfly survival

这种适应性对于蜉蝣的生存至关重要，

since relatively few of these unborn flies are likely to reach adulthood,

因为未出生的小蜉蝣 能长到成虫的并不多，

and even fewer will successfully reproduce themselves.

能成功繁殖自己的就更少了。

In most of these flights, male mayflies form dancing swarms,

在大部分飞行中， 雄性蜉蝣会聚集成舞蹈群，

which female mayflies move through until a male grasps them

雌性蜉蝣穿梭其中， 直到被雄性蜉蝣抓住

for some mid-air mating.

进行空中交配。

Some all-female populations can reproduce without joining in the dance,

有些全雌性群体不用参与舞蹈就能繁殖，

using a process called parthenogenesis to produce viable offspring

她们使用一种称为「孤雌生殖」的程序，

没有雄性的帮助也能繁育后代。

without the help of a male.

And recent research suggests some mayfly populations may even switch back and forth

最近的研究表明，一些蜉蝣甚至可能

在这两种繁殖形式之间来回切换。

between these two forms of reproduction.

But regardless of how the eggs are made ready,

但不论这些卵的来源如何，

the female will deposit them on or under the water,

雌蜉蝣都会把卵产在水面或水下，

and promptly perish.

然后迅速死去。

This might sound like a tragically brief existence.

这像是一个悲剧般短暂的存在，

And even mayflies’ scientific name,

甚至蜉蝣的学名 「Ephemeroptera」

Ephemeroptera, refers to their stunningly short lifespan.

也暗示了它们惊人的短暂寿命。

But for centuries, fishermen suspected that mayflies live much longer

但是几个世纪以来， 渔民们一直怀疑蜉蝣的寿命

than this short flight.

比这短暂的飞行长得多。

And in 1681, scientists finally caught up to their fishing friends

直到 1681 年，科学家们终于 赶上了他们的渔民朋友，

with a published account of the full mayfly life cycle.

发表了一篇蜉蝣完整生命周期的文章。

When the time is right, these eggs will hatch.

当时机成熟时，这些卵就会孵化。

Depending on the kind of mayfly,

视蜉蝣的种类而定，

this can happen as late as several months after the egg is laid,

最迟可能会在卵产下后几个月，

or even before it’s completely left the mother’s body.

或者甚至在它离开母体之前发生。

But whenever their egg opens up,

一旦卵孵化，

the mayfly inside quickly finds its way into fresh water,

里头的蜉蝣会迅速进入淡水中，

and it’s in this aquatic, nymph stage

而正是在这水生的幼虫阶段，

that mayflies spend the majority of their lives.

蜉蝣度过其生命中的大部分时光，

Inhabiting rivers, small streams, ponds, lakes,

栖息在河流、小溪、池塘、湖泊

and other places with clean fresh water,

和其他有干净淡水的地方。

most mayfly species stay in this nymph stage and feed underwater

大多数种类的蜉蝣 都会生活在幼虫阶段

并水下觅食将近一年。

for nearly an entire year.

In fact, some species live as nymphs for up to two years

实际上，有些种类的幼虫期长达两年，

before they metamorphose into their winged adult state.

然后才蜕变进入有翅膀的成虫階段。

A year is a long time for such a small creature to stay alive.

对于这样一个小生物来说， 活一年是很长的时间。

So to survive and thrive, mayfly species have a wide variety of habits

因此，为了生存和繁殖，

蜉蝣有各种各样的习性

and corresponding body forms.

和相应的身体形态。

Sprawlers are flat enough to stick to surfaces

爬行类蜉蝣身体扁平 能粘附在水中物体表面上，

despite the strength of a current,

尽管水流很强也不怕，

while clingers accomplish the same feat with suckers and claws.

而粘附类蜉蝣用吸盘和爪子 也能做到同样的事情。

Other species are swimmers, crawlers, or borers.

其他种类的有游泳、爬行或钻洞类。

One of the most noticeable groups are the burrowing mayflies;

最引人注目的族群之一， 是挖地洞的蜉蝣；

sizable specimens which use their legs, tusks,

这些大小可观的蜉蝣 会利用它们的腿、长牙、

and a scoop on their heads to dig U-shaped tunnels.

和头上的铲子来挖掘 U 形隧道。

In these muddy dwellings, the nymphs use their abdominal gills

在这些泥泞的住处，幼虫会利用腹鰓

来加速水流穿过它们的洞穴，

to accelerate water through their burrow, filtering it for food along the way.

沿途过滤水流以寻找食物。

After they metamorphose, adult swarms can get so large

幼虫蜕变后，

其成虫群可能会变得非常庞大，

they appear on weather radars like rain.

以至于会像雨一样出现在气象雷达上。

Regardless of how they've adapted,

无论它们如何适应，

each unique species plays an essential role in their ecosystem.

每个独特的物种在其生态系统中 都发挥着重要作用。

Plus, nearly all mayflies are a staple of freshwater fish diets,

此外，几乎所有蜉蝣都是淡水鱼的主食，

and since they ingest the smallest particulate matter in their environment,

且由于它们摄入环境中最微小颗粒物质，

mayflies are also very sensitive to water pollution.

蜉蝣对水污染也非常敏感。

In fact, scientists can tell a lot about a water body’s health

科学家们可以判断水体健康状况，

based on which mayfly species they find.

根据发现的蜉蝣种类。

If they don't find mayflies at all,

如果他们根本找不到蜉蝣，

it's usually an indication that something is wrong.

这通常表示出问题了。

So the next time you see a swarm of mayflies over a pond, bridge,

所以下次你在池塘、桥上、 或公园喷泉上看到一群蜉蝣时，

or park fountain,

remember that their short aerial dance

记得它们短暂的空中之舞，

means a healthy world exists below the surface.

意味着水面下擁有一个健康的世界。