Earthworm is a name given to a worm in the class Oligochaeta in phylum annelida. The earthworm has a cylindrical shaped segmented body that tapers off at both ends. Some species are pale red while others are dark brown. Earthworm has bristles called setae that project from their body which it uses to hold to a surface. Some of them grow only about a few centimeters in length, but there are other tropical species that can grow up to 3.3 meters. Some earthworm species can live up to ten years.
With no other type of sense except its sense of touch, earthworm relies on its skin to observe and perceive its surroundings. Earthworms are hermaphrodites with each worm having both male and female reproductive organs. However, they still need a partner to reproduce. Their eggs are buried in earth in cocoons. The cocoons protect the eggs until they hatch as small fully developed worms.
Earthworms live in a moist condition and usually live in the upper layer of the soil. They shun sunlight but usually get to the surface in special situation such as when their burrows are flooded during rains. They usually get out at night to feed and to throw off their castings. They usually feed on organic matter such as dried and decayed leaves in the soil. During hot weather they penetrate downward to avoid dehydration. In burrowing they swallowed soil containing decayed leaves, vegetable and other organic matter.
Species of earthworms can be categorized in three types according to their dwelling places in the soil. The litter dwellers or epegeic species live in fallen dried leaves and other organic matter on top of the soil. They usually consume decayed organic matter. The topsoil dwellers or endogeic species live 2 to 3 inches in the topsoil. They create horizontal burrows and consumes large amount of topsoil and organic matter. The subsoil dwellers or anecic species live 5 to 6 feet in the soil in vertical burrows and need surface crop residue to live. They also consume large amount of soil and organic matter in it.
Earthworms play an important part on the ecology of the soil. They benefit the plants by decreasing or controlling the amount of harmful organism in the soil and by improving its fertility. Plants need air in the soil so that their roots can thrive. The earthworms’ burrowing breaks the compaction of the soil that allows plant’s roots to remove carbon dioxide from the soil. At the same time they also help let in the needed oxygen of the plant in the soil. With the improve soil porosity, plants can now easily absorb water to facilitate its growth. As they burrow, earthworms consume soil and organic matter for food. The combination of soil and organic matter in the earthworm’s gut makes a good fertilizer in the form of castings in or on the surface of the soil when they are excreted. Earthworm castings have higher value of nitrogen, potassium, phosphorus, calcium, zinc and boron contents than the surrounding soil. Earthworms’ castings also improve the soil’s pH level.