Researchers believe that when it rains, the worms come out for migration from one place to another in the search of food, new habitat, or a mate.
Earthworms can not travel during the dry season because of their moisture requirement. Therefore, the rainy season is the best time for them to travel greater distances over soil surface than traveling through the soil.
Scientists also believe that earthworms may feel rain vibrations as predator’s vibrations which cause earthworms to come out of their burrows.
During this migration over soil surface, they might get killed by birds or the sun’s heat.