Why do Earthworms come out in the Rain?
They mainly live underground to avoid sunlight, as sunlight removes the moisture from their skin. They would die quickly if remained exposed to sunlight for a long time. Earthworms need a moist environment for diffusion of gases through their skin. They are often seen above the ground after a heavy rain. There are many theories about this behavior of earthworms. One opinion is that the amount of oxygen dissolved in water is less than that in the air. So, earthworms come above ground when their burrows get filled with rainwater. However, if sufficient amount of oxygen is dissolved in the water, they can live underwater for many days. Another supposition is that the humidity after rain is high, and therefore the earthworms come out as the high humidity protects their skin from dehydration. Besides, they can also move faster on the moist surface, and therefore reach new places for populating. Another reason for coming above ground may be the fact that due to respiratory activities of orga
Earthworms are seen on the surface after large rain storms flood the soil because, despite needing a moist environment to allow the diffusion of gases across their skin membrane, where the soil becomes saturated they begin to drown. To protect themselves they escape to the surface, but if the ground is un-naturally hard they may after become stranded and die from exposure. This is why they are seen in places like driveways after a storm. However, this theory is not applicable to certain earthworm species that can survive immersion for several days in oxygenated water.
