A common sight in the rainy season and after rainstorm is the earthworm crawling and wiggling about. Earthworms are also known as rain worms, big worms, burrowers and dew worms. 8 to 10 inches long, about 2,500 species of earthworms can be found. They are of red, gray or black colors. With a tubular body, they are slimy, moist, with bristles on the body. They are hermaphrodites. A moist environment is needed for the survival of earthworms. They avoid sunlight and so live underground. They would die of prolonged exposure to sunlight. In earthworm, breathing takes place through the skin and a moist environment is required for this. According to one theory, oxygen in water is less than that in air. In the rains, their burrows are filled with rainwater and due to insufficient oxygen they come up above the ground for the increase of intake of oxygen.

According to another theory, earthworms come out after rain due to high humidity, thus protecting the skin from dehydration. It is also assumed that they come on the ground to avoid drowning and suffocation to protect them. Also, the earthworms need to get to new places for the purpose of populating and mating which is difficult underground and the rain provides them moist surface for moving faster up on the ground. According to another theory, the carbon dioxide in their body increases by living underground forming harmful carbonic acid in the rains. Thus, the earthworms crawl on the surface thereby avoiding harmful acidic environment. Thus, the earthworms come up in the rain due to the favorable conditions after a rain.