reported 11 earthworm species in the waste deposit sites of West Tripura out of
which only P. excavatus is a typical vermicomposting species while others have
affinity for organic wastes and play some role in waste degradation and
vermistablization.
11.3 Growth and Reproduction in Earthworms Used
for Vermicomposting and Vermistabilization
Earthworms are hermaphrodite with separate testes and ovaries. Most of the earthworm species reproduce by cross-fertilization, although some species produce
cocoons parthenogenetically or by self-fertilization. Following copulation, which
may take as long as an hour, the worms separate and each clitellum produces a
secretion that eventually hardens over its surface. When it gets hard, the partners
move backward, so drawing the tube over its head, and when the worms are
completely free, the ends of the tube close to form the cocoon which is roughly a
lemon-shaped structure but with a shape typical of each species (Fig. 11.1) (Edwards
and Bohlen 1996). Fertilization which occurs in the cocoon is thus external. From
the cocoon, after a certain period of development (incubation period), baby worm
emerges out (Fig. 11.1 and 11.2).
According to Hyman (1940), earthworms grow continuously throughout their
lives by the addition of segments proliferated from a ‘growing zone’ in front of the
anus. Edwards and Bohlen (1996) supported the view of Evans (1946) who opined
that some earthworm species possess the adult number of segment on hatchling,
whereas other species add further segments during post-emergence growth. In
earthworms, there is a pre-reproductive growth phase followed by a phase of
reproduction after attainment of sexual maturity. Many workers have confirmed a
sigmoid growth curve for E. fetida and in other species that grow in organic wastes
(Edwards and Neuhauser 1988). Rate of growth and reproduction of some epigeic
earthworm species utilized in waste degradation are shown in Table 11.1.
11.3.1 Perionyx excavatus (Perrier 1872)
Potential of P. excavatus for breaking down of organic waste was first reported by
Kale et al. (1982). This tropical earthworm species is commonly found over a large
area of tropical South Asia (Stephenson 1930; Gates 1972) although it has also been
transported to Europe and North America. This native epigeic species lives solely in
organic wastes (preferably cattle dung) with adequate moisture content (50–60%)
and organic matter (4.5–12%) (Bhattacharjee and Chaudhuri 2002). This earthworm
species has high fecundity (150 cocoons worm
À1 year
À1 ) with a short life cycle of
40–50 days. Its cocoon development time is 13 days (Bhattacharjee and Chaudhuri
182
P. Chaudhuri and S. Debnath
which only P. excavatus is a typical vermicomposting species while others have
affinity for organic wastes and play some role in waste degradation and
vermistablization.
11.3 Growth and Reproduction in Earthworms Used
for Vermicomposting and Vermistabilization
Earthworms are hermaphrodite with separate testes and ovaries. Most of the earthworm species reproduce by cross-fertilization, although some species produce
cocoons parthenogenetically or by self-fertilization. Following copulation, which
may take as long as an hour, the worms separate and each clitellum produces a
secretion that eventually hardens over its surface. When it gets hard, the partners
move backward, so drawing the tube over its head, and when the worms are
completely free, the ends of the tube close to form the cocoon which is roughly a
lemon-shaped structure but with a shape typical of each species (Fig. 11.1) (Edwards
and Bohlen 1996). Fertilization which occurs in the cocoon is thus external. From
the cocoon, after a certain period of development (incubation period), baby worm
emerges out (Fig. 11.1 and 11.2).
According to Hyman (1940), earthworms grow continuously throughout their
lives by the addition of segments proliferated from a ‘growing zone’ in front of the
anus. Edwards and Bohlen (1996) supported the view of Evans (1946) who opined
that some earthworm species possess the adult number of segment on hatchling,
whereas other species add further segments during post-emergence growth. In
earthworms, there is a pre-reproductive growth phase followed by a phase of
reproduction after attainment of sexual maturity. Many workers have confirmed a
sigmoid growth curve for E. fetida and in other species that grow in organic wastes
(Edwards and Neuhauser 1988). Rate of growth and reproduction of some epigeic
earthworm species utilized in waste degradation are shown in Table 11.1.
11.3.1 Perionyx excavatus (Perrier 1872)
Potential of P. excavatus for breaking down of organic waste was first reported by
Kale et al. (1982). This tropical earthworm species is commonly found over a large
area of tropical South Asia (Stephenson 1930; Gates 1972) although it has also been
transported to Europe and North America. This native epigeic species lives solely in
organic wastes (preferably cattle dung) with adequate moisture content (50–60%)
and organic matter (4.5–12%) (Bhattacharjee and Chaudhuri 2002). This earthworm
species has high fecundity (150 cocoons worm
À1 year
À1 ) with a short life cycle of
40–50 days. Its cocoon development time is 13 days (Bhattacharjee and Chaudhuri
182
P. Chaudhuri and S. Debnath