Earthworms are among the most ancient of terrestrial animal
groups. Originally they were marine animals. Fossils of Polychaete worms have
been found in South Australia in Precambrian sediments 630-570 million years
old. Today's earthworms belong to the Oligochaetes. The limits of evolutionary
and ecological diversity must be defined by inherent limitations of their
mechanical "design" and behavioral and physiological adaptability.
Earthworms are traditionally used in domestic compost heaps and
earth toilets. People are now looking for ways to dispose of domestic and
industrial wastes without polluting the environment. This has sparked interest
in using earthworms for large-scale waste disposal. Worms are thus seen as a
biological resource for rural development. Maintaining the diversity of
resources such as worms will help ensure a resource base for future technologies
such as vermicomposting.
The practice of using earthworms for composting is known as
vermicomposting. Not all earthworms are useful for vermicomposting. Earthworms
are classified into two groups:
(detritivores) - useful for vermicomposting
· Humus-feeders (geophagous) -
useful for soil turnover and tillage. Worms used for vermicomposting should have
· Able to live in active
· Tolerate extreme changes in
· Multiply fast, undergo rapid
incubation, and mature quickly.
· Digest well and have such
enzymes as cellulase and chitinase in their gut.
Aristotle described earthworms as "intestines" of the earth.
Charles Darwin wrote about earthworms, "it may be doubted where there are many
other animals which have played so important a part in the history of the world
as have these lowly organized creatures."
· Surface dwelling
· Red color
on nearly 90% fresh organic matter and 10% soil
· Harnessed for vermicomposting
· Deep burrowing
· Pale color
on nearly 90% soil and 10% nearly degraded or humified organic matter
· Useful in making the soil porous and mixing and
distributing humus through soil
Humus former and feeder
Species useful for vermicomposting are:
Effects of vermicomposting on indigenous species
It is not possible to use both exotic and endemic humus-forming
species for vermicomposting. Exotic species multiply very rapidly and outgrow
the endemic species.
However, using humus-forming exotic species for vermicomposting
can be useful. Fast turnover of organic matter by these humus-formers produces
food rich in bacteria and humus for the indigenous humus-feeders. The
humus-feeders can then multiply very fast under vermicompost heaps and after the
compost is added to the field, stimulating their soil processing activities such
as aeration, tunneling and soil turnover.
Vermicomposting for rural sanitation
Earthworms can be used to process human faeces. Vermiculture may
be particularly useful for treating sewage in rural areas. Research has shown
that some types of bacteria found in faeces, Serratia marcessens and Escherichia
coli, are killed when they are ingested by the earthworm L. terrestris. The
worms reduced numbers of the pathogen Salmonella erteriditis to a level of
2000-fold less, possibly because of competition from the endemic microflora of
the worm gut.
Earthworms aerate sewage sludge and speed its drying, thereby
favouring aerobic bacteria. Since most human enteric pathogens are anaerobes,
sludge condtioning by earthworms can be beneficial from the public health
standpoint. More research is needed on the effect of vermicomposting on other
enteric bacteria, pathogenic viruses and parasites.
In villages in India, vermicomposting of latrine waste mixed
with other agricultural waste can help dispose of sewage and produce valuable
compost that can increase soil fertility and agricultural production.
Vermicomposting for rural sanitation
Vermicomposting of sewage sludge
· Aerobic sludge ingested by E.
fetida is decomposed and stabilized about three times as fast as non-ingested
· Objectionable odors disappear
· Marked reduction in
populations of Salmonella enteriditis and other Enterobacteriaceae.
· Anaerobic sludge and sun-dried
sludge is toxic to E. fetida.
· Sewage sludge can be, mixed
with cellulosic and lignin-rich wastes.
· Earthworms, which accumulate
heavy metals and agrochemicals from sewage, may be environmentally hazardous if
used as protein source.
Practical applications of biodiversity
Symbiotic relationship between
detritivorous worms and micro-organisms
· Population of India is
· The average person produces an
average of 1/2 kg of excrete every day.
· 4,000,000 kg of night soil, if
vermicomposted, would yield 2,000,000 kg of humus-rich organic compost a day.
· Considering the night soil of
the 70% of the population living in villages, nearly 1,400,000 kg vermicompost
could be prepared every day.
Prepared by Dr.