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After a heavy rainstorm, you've probably seen worms popping out of the soil,
大雨过后，你也许能看到蠕虫类动物从泥土中钻出来，
getting stranded all over sidewalks and parking lots.
占领人行道和停车场。
But between birds, clumsy humans, and the sun, it's dangerous for a worm to climb out of its safe, cozy burrow.
可是爬到满是鸟类、行人和阳光的陆地上，其实对于蠕虫类动物来说，爬出自己安全舒适的洞穴是很危险的。
And yet they suddenly abandon ship whenever it starts raining.
但是一开始下雨，它们就突然弃船而逃了。
Scientists have come up with plenty of possible reasons why rain might trigger this behavior.
科学家们提出了很多种可能解释为什么下雨会刺激它们的这种行为。
But they don't quite agree on all of them.
但是他们并未达成一致意见。
The oldest hypothesis -- and the one you might've heard -- is that earthworms surface to avoid drowning.
最古老的一种假设—你也许也听过—蚯蚓爬出来是为了避免溺水。
That's because worms take in oxygen through their skin in a passive process called diffusion,
那是因为蠕虫以一种被动的过程—渗滤，从皮肤摄取氧气，
where oxygen moves from the higher concentration outside their bodies to the lower concentration inside.
在这种过程中氧气从身体外边的高浓度移动到内部的低浓度。
When soil floods after a rainstorm, worms can usually still breathe if there's enough oxygen dissolved in the water.
雨后土壤被淹没，蠕虫还是可以呼吸，前提是水中有充足的氧气。
But water is a lot denser than air, so diffusion is much slower -- like, up to 1000 times slower.
但是水比空气密度大，因此渗滤过程更慢—比如，其速度可以慢上1000倍。
Which means that for a worm, it could be a lot harder to breathe after a downpour, which could make them rush to the surface.
对蠕虫来说，这意味着雨后呼吸更加困难，因此它们匆忙逃到陆地上。
But some biologists have pointed out that plenty of worms can actually live for days submerged in water
但是一些生物学家指出，很多蠕虫可以潜入水中生活很多天，
although some of that may depend on the species.
但是这或许要取决于蠕虫的种类。
One study published in 2008, found that two different species of worms use different amounts of oxygen.
2008年发表的一项研究发现，有两种蠕虫需要的氧气量不同。
A common tropical worm uses relatively little, so it doesn't come up to the surface after it rains.
一种热带常见蠕虫需要氧气相对较少，因此这种蠕虫不需要在雨后爬上陆地。
But another worm, the Alabama Jumper, needs more oxygen, especially at night, and it does surface.
但是另一种蠕虫Alabama Jumper，则需要更多氧气，尤其是在夜晚，而且它们确实会爬上陆地。
So, there may be worms who do need to surface to breathe -- or at least prefer to -- while others don't.
所以有些蠕虫确实需要爬上来呼吸—至少它们更喜欢这样—而有一些则不需要。
Other experts think worms might surface for different reasons.
其他专家认为蠕虫爬上来的原因并不相同。
They argue that worms flee their burrows because rain gives them great travel conditions.
他们认为蠕虫逃离自己的洞穴是因为雨水给了它们更好的爬行环境。
Earthworms move faster above ground, and they can crawl more quickly and safely when it's wet because they're less likely to dry out.
蚯蚓在地上快速移动，并且地面潮湿时，他们可以爬的更快也更加安全，因为它们不会被烤干。
Some scientists have also proposed that worms take flooded soil as a cue to mate,
一些科学家也提出蠕虫将淹没的土壤当做交配的暗示，
possibly to increase their chances of finding a partner, but that seems to be limited to nightcrawlers and a few other species.
可能会增加它们寻找到另一半的机率，但是这似乎仅限于夜晚爬行者和几种其他种类。
One last hypothesis is that raindrops landing on soil create vibrations similar to those
最后一种假设是落入土壤的雨滴创造了一种振幅，
made by one of the earthworm's biggest predators: the mole.
这种振幅和蚯蚓最大的敌人—鼹鼠所制造出的振幅一样。
It's definitely true that earthworms will book it to the nearest exit if they sense certain tremors.
当蚯蚓感应到某种震颤时，它们会从最近的那个出口逃离，这绝对是真事。
People actually exploit this by going worm grunting,
人们会通过一种worm grunting（通过声音抓蠕虫）的方式来抓蠕虫
where they catch worms to use as bait by driving stakes into the ground and vibrating them.
这种方法是将棍子插入途中并振动棍子，所抓到的蠕虫被用作诱饵。
But experiments suggest that worms are only sensitive to vibrations that mimic moles, and that falling rain doesn't do the trick.
但是实验证明，蠕虫只对模仿鼹鼠的振幅敏感，雨滴并不管用。
So, we may not know for sure why earthworms grace us with their presence after a storm,
因此，我们或许并不能够确定为什么蚯蚓会在雨后出现，
but at least we know what to do if we want to go fishing.
但是至少我们知道如果我们想去钓鱼该怎么办。
Thanks to patreon patron Miranda McCarthy for asking this question, and thanks to all our patrons, who keep these answers coming.
感谢patreon赞助人Miranda McCarthy的提问，感谢所有赞助人一直向我们提问。
If you'd like to submit a question to be answered, you can go to patreon.com/scishow.
如果你想提问，请登录patreon.com/scishow。
And don't forget to go to youtube.com/scishow and subscribe!
不要忘记订阅我们的频道！
