The soil ecosystem
supports the most vital components of plants and
animal life necessary for human developments. While
the management of the cultivated soil has traditionally
been dependent on water and fertilizers, the role
of biotic components has not been fully evaluated
and integrated in the management strategies. Earthworms
constitute one of the vital groups of any faunal
element in the soil and their role in maintaining
the fertility of soil system is being increasingly
acknowledged. India has a large earthworm resource
both in faunal diversity and numbers. However, rearing
of earthworms for practical application such as
restoration of degraded soil systems and improving
of existing condition have rarely been attempted
on a commercial basis. The technology of Vermiculture
as such needs to be standardized. In the present
article, the lifecycle, ecology, different methods
of vermicomposting and the role of earthworms in
composting are discussed.
1. Role of Earthworms:
Earthworms belong to the order Oligochaeta under
the phylum Annelida. They make a large contribution
to the total weight or biomass of invertebrates
in soil, particularly in temperate regions. Through
its characteristic functions of breaking, grinding,
churning, assimilating and tunneling, earthworms
have proved to be soil’s digestive system.
Through its buffering action, it helps to maintain
the soil in the natural pH range. In humid regions,
earthworms are one of the most potent agencies of
nature, bringing about continuous renewal and maintenance
of the important surface layer upon which life depends.
2. Taxonomy:
Earthworms are classified into 10 families, comprising
240 genera and about 3320 species. However, many
areas still remain to be studied and the discovery
of new species cannot be overruled. So far, Indian
earthworm fauna is reported to comprise 509 species
belonging to 67 genera. In general, earthworms are
divided into two groups viz., Microdrilli worms
– which are aquatic and represented by 280
species and Megadrilli worms – which are terrestrial
and are called earthworms. Earthworms are also
classified on the basis of their burrowing habits
and life style, as epigeics, endogeics and anecics.
Epigeics are surface litter dwellers and have
uniform colouration. They feed on partially decomposed
organic residues converting them to colloidal
amorphous compost. Endogeics live in the upper
30 – 50 cm soil. They are lightly pigmented
and vary in size. They construct horizontal branching
burrows and feed on organic residues together
with soil particles. Anecics construct vertical
tunnels and emerge in the night to leave their
castings and also to collect organic materials
for feeding.
3. General body
structure:
Earthworms have a long cylindrical body, which
is divided externally into bands or segments,
which coincide with the position of the internal
septa. Clitellem is a glandular portion of the
epidermis associated with reproduction and is
recognizable in the adult worm. Setae, which are
bristle – like and borne on the exterior
of the body, are used to grip the substrate and
for locomotion.
The alimentary canal or gut is basically a tube
extending from the mouth to the anus. Muscular
contractions of the gizzard grind the food with
the aid of mineral particles taken in along the
food into micro particles. The rest of the alimentary
canal is the intestine. A number of enzymes such
as protease, analyses, lipase, cellulase and chitinase
are secreted in the intestine. They mix thoroughly
with the churned food materials. The enzymes present
in the earthworm cast continue to break down the
undecompensed organic residues. Terrestrial earthworms
have no specialized respiratory organs. The cuticle
of the body wall is kept moist by the secretion
of the mucous glands of the epidermis. The mucus
should not dry up to ensure proper respiratory
activity of the worms. Hence the medium in which
worms thrive should always remain moist.
Fertilization as a rule in earthworm is cross-fertilization,
i.e., ova of one individual are fertilized by
sperms of another individual. After fertilization,
the cocoon or the egg capsule is formed from clitellar
gland. The capsule or cocoon is a fleshy container,
which is formed in the clitellum: it is filled
with albumen and contains two or three eggs floating
in it. The cocoons differ greatly in size , shape,
colour and number of eggs according to species.
Hatching takes place under favorable conditions.
After a certain period the young worm reaches
its sexual maturity. Generally the formation of
clitellum indicates sexual maturity and adult
stage. Average life period of earthworms is about
fifteen years.
|
