Why Do Earthworms Come Out in the Rain?

After reading this post from the internet, now I know why and now I know more and more about our slimy friend called earthworms. Very interesting don't you think?

Imagine having the ability to regenerate a part of your body, breathe through your skin instead of a nose, have 5 hearts and tell whether this land is fertile or not. You would think you were a superhero straight out of marvel comic books but these qualities I have enumerated are just the basic characteristics of earthworms.
Earthworms are under the subclass oligochaete of the phylum Annelida. They live in the ground to steer clear from sunlight that dehydrates them. Hunted by predators both in land (birds, moles, etc) and water (used as bait for fishing), they have evolved into hermaphrodite critters (having both male & female reproductive organs).
Very fascinating creatures; do not be surprised when you see an earthworm above ground after heavy rain. There are many speculations why this occurs. The simplest reason that my 5 year old nephew hypothesized was that they just want to avoid drowning which actually does make sense. My take is that during heavy rain, the soil becomes eroded which causes earthworms to get displaced above ground.

Others believe that the amount of oxygen dissolved in rain water is lesser than the air. What this means is that they come above ground when the soil gets water clogged but in cases where there is enough oxygen dissolved, there wouldn’t be a need to resurface.
Another theory focuses more on the humidity. After heavy rain, the humidity level is high. This enables the earthworms to have protection from the sun and allows them to travel on the surface to repopulate in another area.
This makes sense too because it is easier for them to crawl on moist soil compared to dry. Some believe that to protect themselves from the acidic environment caused by other living organisms underground, earthworms escape to top soil where they can get away from the carbon dioxide increase. Whatever specific reason they might have, it’s good that they do because every time they emerge from their burrows, they loosen the soil which facilitates its aeration (when air circulates within a substance) for better soil productivity.