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Why do worms come to the surface when it is raining ?
Answer 1:

I used to ask myself the exact same question every time it rained. The reason why earth worms come up to the surface of the soil when it rains is because if the worms do not, they will drown. Worms are animals and, like you and me, they require oxygen to live. Instead of breathing air though their mouth into lungs, worms absorb oxygen from the air across their skin. Worms eat dirt. They burrow into the soil and normally live underground, where they are protected from the sun and so won't dry out. If you've ever played in the dirt by digging holes, you probably noticed that there are small holes or tiny pockets of air. The worms use that air, and the air that enters through their burrow holes, to breathe. When it rains and the dirt absorbs a lot of water, those air holes disappear, and the worms' burrows fill with water. If the worms do not come to the surface during a heavy rain, they will suffocate. Likewise, if they do not return to the soil after the sun comes out, they will dry out and die.
Worms are very important for plants, because they improve the soil by introducing air and by recycling nutrients. I hope I answered your question!

Answer 2:

A great observation.As you probably know, earthworms, as the common name implies, live underground, and like most terrestrial creatures, breath air. Oxygen uptake, however takes place through the body wall, as earthworms lack lungs. When it rains, the water flows into their burrows (their wormy homes), blocking off their air supply. As you can imagine, this causes the worms a considerable amount of stress. So, the earthworms that you see during or after a big rain are those that either fled to the surface for a breath of air or those that drowned and were washed from their burrows (poor worms).

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