Vermiculture in Egypt: - FAO - Regional Office for the Near East and

2.1.3. Moisture
The bedding used must be able to hold sufficient moisture if the worms are to have a
livable environment. Earthworms do not have specialized breathing devices. They
breathe through their skin, which needs to remain moist to facilitate respiration. Like
their aquatic ancestors, earthworms can live for months completely submerged in
water, and they will die if they dry out (Sherman, 2003). The ideal moisture-content
range for materials in conventional composting systems is 45-60%. In contrast, the
ideal moisture-content range for vermicomposting or vermiculture processes is 70-
90%. Within this broad range, researchers have found slightly different optimums:
Dominguez and Edwards (1997) found that there is a direct relationship between the
moisture content and the growth rate of earthworms. E. andrei cultured in pig manure
grew and matured between 65 and 90% moisture content, the optimum being 85%.
Until 85% moisture, the higher moisture conditions clearly facilitated growth, as
measured by the increase in biomass. Increased moisture up to 90% clearly
accelerated the development of sexual maturity, whereas not all the worms at 65-75%
developed a clitellum even after 44 days. Additionally, earthworms at sexual maturity
had greater biomass at higher moisture contents compared to worms grown at lower
moisture contents. Canadian researchers in Nova Scotia tested moisture contents with
different bedding materials, i.e. organic materials included shredded corrugated
cardboard, waxed corrugated cardboard, immature municipal solid waste compost,
biosolids (sewage sludge), chicken manure and dairy cow manure in a variety of
combinations. They found that 75-80% moisture contents produced the best growth
and reproductive response (GEORG, 2004).
The moisture content preferences of juvenile and clitellate cocoon-producing (adult)
E. fetida in separated cow manure have been investigated. It ranged from 50% to 80%
for adults, but juvenile earthworms had a narrower range of suitable moisture levels
from 65% to 70%. Clitellum development occurred in earthworms at a moisture
content from 60% to 70% but occurred later at a moisture content from 55% to 60%.
The tolerance limit for low moisture conditions on the growth of E. fetida was
reported to be below 50% for up to 1 month (Reinecke and Venter, 1987). While
Gunadi et al. (2003) found that the earthworm growth rate was fastest in the separated
cattle manure solids with a moisture content of 90% with a maximum mean weight of
earthworms of 600 mg after 12 weeks. The slowest growth rate of E. fetida was in the
separated cattle manure solids at a moisture content of 70%.
2.1.4. Aeration
Worms require oxygen and cannot survive anaerobic conditions (very low or absence
of oxygen). When factors such as high levels of grease in the feedstock or excessive
moisture combined with poor aeration conspire to cut off oxygen supplies, areas of
the worm bed, or even the entire system, can become anaerobic. This will kill the
worms very quickly. Not only are the worms deprived of oxygen, they are also killed
by toxic substances (e.g., ammonia) created by different sets of microbes that bloom
under these conditions. This is one of the main reasons for not including meat or other
greasy wastes in worm feedstock unless they have been pre-composted to break down
the oils and fats.
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