Why do earthworms come out in the rain

Earthworms, also called nightcrawlers, belong to the phylum Annelida and the class Oligochaeta. In layman’s terms, this means they are known as burrowers. This is because direct sunlight is directly fatal to earthworms, as the UV rays from the skin severely damages their moist exterior. Because of this relationship with the sun, its often wondered why these burrowers bother to come out during a rain storm.

There have been numerous stories and theories developed in order to explain the unique behavior of earthworms in a rain storm. One of the most popular of these theories is that during a rain storm, the balance of oxygen underground is affected drastically, leaving the earthworm with no option but to surface to breathe as the ground becomes more sodden. Many scientists have generally accepted this as the cause of an earthworm’s appearance during a rain storm, but it is not the only accepted theory.

Another theory surrounding this phenomenon is that it is the best time for worms to move from place to place. Since clouds are blocking the sun, worms have an easier time getting around and because the soil is soft, it is much easier to burrow through. Some scientists believe rain storms are when earthworms take the opportunity to set up new colonies in completely different locations, which is very important to their survival if one location becomes overcrowded. Since most predators don’t venture out into the rain, earthworms are relatively safe as they are on the move.

An additional theory, though less widely supported, is that rain water causes soil to become acidic, meaning staying underground would become fatal for the earthworm. According to this theory, earthworms surface to prevent dying from acidic soil. Currently, there is no evidence to support this theory, as soil tested showed only minor changes in pH.

While there is no definitive cause as to why earthworms come out when its raining, it is known that when these creatures leave the soil, they leave behind their passage ways, which makes it easier for minerals and other nutrients to get down deep into the soil. Because of this, the burrowing and resurfacing behavior of exhibited by earthworms is important for healthy soil in an area. In fact, soil which is laden with earthworms working it are said to be richer in nitrogen and phosphates, which is why many gardeners actually transplant these creatures into their tilled soil.