Earthworms are one of the most useful animals. They are reddish brown in colour and inhabit in upper layers of moist soil. They are generally found under fallen logs, decaying dead leaves and areas with heavy vegetation. They prefer to live in moist condition as it facilitates respiration and also helps them to easily make their way out through the soil. During day time they generally live in the burrows which they make by swallowing the soil. Earthworms have long cylindrical body having more than hundred short segments. They belong to phylum annelida of animal kingdom. Earthworms are very interesting animals and their anatomy and morphology is quite fascinating. Earthworms are hermaphrodite i.e. have both the sexes in the same individual. In case of mature worms the 14-16 are covered by a prominent dark tissue and this part is called clitellum. This clitellum is used to preserve the cocoon.
Earthworms have a unique characteristic of regeneration. They can regenerate its lost body parts. When under the ground, earthworms travel by passing a continuous wave of muscular contractions through their body. This wave alternately decreases and increases the size of the body which help it to make its way through the soil. Earthworms have complete digestive system which is characterised by the presence of special internal fold called typhlosole which helps in increasing the effective surface area for the absorption of the digested food. Earthworms do not have any special structure for respiration. The air is taken in by the process of diffusion for which earthworms are required to have permeable skin. One of the most fascinating features of earthworm is that it has five hearts.
These hearts are present in the form of rings coiled around a gland called calciferous glands. These glands are required to maintain the calcium level in the body of earthworm as they swallow a lot of calcium in the form of soil when they make their way through the soil. Earthworms prove to be very helpful creatures to increase the efficiency of soil. While moving through the soil they make small passageway by swallowing the soil. These passageways are like holes and are very important as water and air required by the roots of the plants can circulate through these holes made by the earthworms. Also in doing so they feed on the nutritive compounds present in the soil, they absorb the nutritive material from the soil and excrete out the rest of the material. Earthworms also increase the fertility of soil by adding nutrients into it. The faecal matter of earthworm called castings are deposited into the soil, these castings are rich in nutrients and increase the fertility of the soil.
Castings of earthworm are rich in nitrogen, phosphorus, calcium and magnesium compounds which increase the fertility and efficiency of the soil. Earthworms are highly useful animals having interesting physiology and anatomy which are present everywhere in soil and are very useful in increasing its fertility.
