為何蚯蚓總是在下雨後出現?

Why do earthworms surface after rain?

Not because they might drown. People often claim that this is the explanation,yet earthworms breathe by exchanging oxygen and carbon dioxide through their skin, which they keep wet with a slimy mucus. This means they are happiest in damp soil and most species can survive for several days under water.So a brief rainstorm should not bother them.Indeed, they may even exploit the wet weather to travel longer distances than they would normally be able to underground.

Some may need to come to the surface to mate when it is wet enough,but only a very few of the 4400 known species of earthworms do this. Another possibility is that earthworms confuse the sound of rain with a predator, such as a mole, and so make their way upwards to the surface to escape.Certainly the animals are well known to respond to such sounds, as any worm catcher will tell you.Some old tricks include vibrating sticks,saws on wooden stakes. And, more bizarrely, giving worms tea and beer.

蚯蚓並非因為可能淹死才爬上地表，人們通常認為那是唯一且正確的答案。然而，事實上蚯蚓藉由濕潤且充滿黏液的皮膚交換氧氣與二氧化碳來行呼吸作用。這代表他們最樂於在泥坑中弄髒自己，同時蚯蚓也是這世界上能在水底中堅持最久的物種，它們能在水底生存數天之久!

因此，一場短促的風雨照理說不會影響他們的在地底生活。恐怕並非如此，蚯蚓們也許會特地選擇在潮溼的天氣中出來冒險，這是因為比起平常穿梭於地底的路線，蚯蚓們在潮溼的天氣能在地表上行走更多更長的距離。

當天氣夠潮濕時，某些種類的蚯蚓為了交配會鑽出地表。不過在已知的4400種蚯蚓中只有極少品種會做出這種行為。另外，蚯蚓們探出地表還有可能是因為它們將雨聲誤認為獵食者，比如說:鼴鼠，而當蚯蚓們在地表時比較容易逃離獵食者的追獵。

毫無疑問的，在蚯蚓殺手圈中，蚯蚓這種動物以對各種聲音十分敏感，且樂於回應而聞名。一些過時的老技倆，如使勁地搖晃木樁或是切割木樁的聲音，以及，更為奇怪的聲響都會使蚯蚓探出頭來瞧瞧外面到底發生了甚麼事!

巴友tcss0612(光山-kohinoor) 提供我末段正確的解釋，真是感謝~