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IN UZBEKISTAN, convoys of lorries bring them vast distances to improve
the desert soil. In the Scottish hills, they helped a sheep farmer to increase
the size of his flocks by half. And in Wales they are restoring land scarred
by open cast mines. The vital ingredient in each case is the earthworm.
Scientists, farmers and entrepreneurs throughout the world are beginning
to realise the worm’s worth.

On any hectare of well-managed farmland there may be twice the weight
of earthworms burrowing through the soil than livestock standing on it:
Charles Darwin described worms as ‘Nature’s ploughshare’. Darwin realised
the value of the earthworm after years of observation. In December 1842,
Darwin spread broken chalk on a field of permanent pasture near his home.
Twenty-five years later, he dug a trench across the field and found a layer
of white nodules of chalk some 20 centimetres beneath the surface. Darwin
concluded that earthworms had thrown up a fine ‘mould’ of earthworm casts,
burying the chalk at a rate of 5 millimetres a year. It is difficult to
imagine even Darwin persuading the research councils to fund an experiment
lasting so long these days. Yet it was through such work that Darwin developed
a theory about the importance of earthworms that revolutionised the study
of soil ecology in much the same way as his theory of natural selection
altered the whole of biology.

Researchers have since confirmed Darwin’s ideas about the earthworm’s
role in improving the fertility of the soil . More recently, scientists
and farmers have begun to manage earthworms to increase the productivity
of agricultural land. And, imaginations fired by the idea of the working
worm, many have begun to look at new ways to exploit worms: in waste disposal,
as a means of monitoring pollution, and as a producer of composts.

Agronomists in New Zealand were the first to actively manage earthworms
on a large scale on agricultural land. When sheep farmers cleared the native
antipodean scrub and replaced it with grassland, they failed to achieve
the high productivity of equivalent land in Europe. In the early 1940s,
one farmer noticed that his pasture was of better quality in the fields
next to his orchard. These fields had a large population of European earthworms
which seemed to be spreading outwards from the orchard and replacing the
native species. The new species of earthworm had been accidentally introduced
into New Zealand in soil brought with plants in the early days of the colony.

Murray Stockdill, of the Ministry of Agriculture in New Zealand, carried
out experiments in the 1960s and 1970s that confirmed that it was indeed
the earthworms that increased the productivity of the pasture. In the absence
of earthworms a thick mat of dead plant material built up on the surface
of the turf. The introduced earthworms began to feed on this material, breaking
it down, mixing it with the soil and releasing nutrients that were locked
up in the dead plants. The first flush of extra nutrients increased the
production of grass by 70 per cent. But once all the extra nutrients were
consumed, the rate of production fell, levelling off at about 30 per cent
higher than normal. This increase in productivity can be attributed to the
general improvements worms make to the structure of the soil. These results
were enough to encourage Graeme Garden of the Lincoln College Agricultural
Engineering Institute, in New Zealand, to develop a turf-cutting machine
to distribute earthworms from areas with large populations to pastures short
of worms.

Dutch polders reclaimed from the sea also suffer from a lack of earthworms.
In 1971, Miendect Hoogerkamp and his colleagues at the Wageningen Agricultural
University, introduced earthworms to polders, and followed their progress
for a decade. The worms made several improvements. Previously, when cattle
and sheep grazed on the polders, the grass sward became detached from the
surface of the soil. Without worms, a layer of organic matter built up on
the surface, and the tramping of livestock compacted the soil below. The
roots of the grass penetrated only the shallow layer of organic thatch,
so that the ripping action of grazing animals separated the turf from the
soil.

Infrared photographs of Hoogerkamp’s experimental plots provided clear
evidence that earthworms broke down the organic matter on the surface. The
plots with worms were warmer at night and cooler during the day than areas
without worms. The wormless plots show much larger fluctuations because
the accumulated thatch reduced the exchange of heat between the soil and
the air. On the polders, earthworms increased yields of grass by 10 per
cent, not as much as in New Zealand, but enough to persuade farmers to abandon
their traditional practice of regular ploughing and reseeding to maintain
production.

The Soviet Union has also realised the potential of earthworms. In the
republics of Turkmenia and Uzbekistan the desert soils require irrigation
to produce high yields of arable crops. Irrigation changes the soil from
one that is inhospitable to earthworms to one where they thrive. Scientists
in the Soviet Union have assisted the slow natural spread of earthworms
by programmes of inoculation, transporting sacks of soil from a riverbank
richly endowed with worms in convoys of lorries.

Earthworm transplants are not confined to scientific research programmes.
Bruce Marshall, a farmer in the uplands of Scotland, improved yields on
his farm by a combination of inoculating his land with worms, adding lime
to the soil and reseeding with clover. The larger population of earthworms
has attracted moles, whose criss-cross runs through the soil thus removing
the need to install artificial drainage. Marshall’s land now supports almost
50 per cent more sheep. Marshall also thinks that earthworms are valuable
in conservation, providing food for nesting waders, game birds, foxes and
badgers.

Not all soils benefit from extra earthworms. Usually only areas with
problem soils show real economic improvements. But whereas farmers look
for an increase in profits, this is not a priority in many projects to reclaim
damaged land. Whatever the nature of the project, most share a common problem:
the topsoil returned to the site is usually very poor. For example, in opencast
coal mining topsoil is usually stored in huge piles for a decade or more
until the mine is worked out. In those 10 years most animals within the
pile die and the soil becomes compacted and structureless.

John Scullion and his colleagues at the University College of Wales
Field Laboratory at Penygroes, Dyfed, studied the rehabilitation of reclaimed
opencast sites. The lack of structure in the soil makes reclaimed fields
prone to waterlogging and damage by trampling. Scullion found that a key
process in improving the site was the slow but sure increase in the number
of earthworms recolonising the sites, which is encouraged by adding large
amounts of organic matter to the land. This suggests that one way to improve
reclaimed land is to add both worms and organic matter. But there are obstacles
to such a technique. The practice in New Zealand of placing turfs containing
earthworms across a field is too expensive and too slow. The solution lies
in culturing earthworms to provide the enormous numbers needed to spread
over a reclaimed site.

Profiting from producing the right numbers

This is not as easy as it sounds. Earthworms in the soil live at low
densities. The earthworms that you find in a compost heap can be cultured
easily in huge numbers. Unfortunately, ‘compost’ worms survive only a short
time when spread on the surface of the soil, away from their rich organic
home.

Kevin Butt and Jim Frederickson, of the Open University, are tackling
the problem of how to produce large quantities of earthworms. By defining
the needs of worms precisely, they hope to provide them with the best possible
conditions for keeping worms at high densities. The economic stakes are
high. Earlier this year, The Guardian reported that the London Regeneration
Consortium has placed an order for several tonnes of earthworms to improve
the quality of 50 hectares at King’s Cross, London, as part of a redevelopment
programme costing Pounds sterling 6 billion. Quite where such huge quantities
of earthworms will come from is a different story.

If you turn over a well kept, mature compost heap you will expose many
earthworms, most with a deep red pigmentation. The concentration of earthworms
reflects the richness of the food supply in a compost heap. In soil, fragments
of organic matter and associated microorganisms are dispersed among the
mineral particles. The species of worms in compost normally live in habitats
that are rich in organic matter: among leaf litter in woodlands, within
the grass thatch of pastures and under decaying logs and piles of dung.

The fact that high concentrations of earthworms could be made to grow
in organic materials was not lost on early backyard entrepreneurs in the
US. The spur, in their case, was the large market for bait that was developing
as fishing became a popular sport in the 1930s and 1940s. From this, ‘earthworm
farming’, or vermiculture, was born. Unfortunately the most commonly cultured
worm, a species called Eisenia fetida, makes very poor bait. E. fetida earned
its name from its defence mechanism: when threatened, when it is put on
the end of a hook for instance, it discharges a noxious yellowy, fetid-smelling
fluid. Fish find E. fetida unpalatable. Soil-dwelling species, such as Lumbricus
terrestris, make much better bait. Commercial bait companies now employ
specialist worm pickers to roam over golf courses and other green open spaces
plucking earthworms from the surface and placing them in tins attached to
each ankle.

The fact that E. fetida was useless as bait did not stop the barnyard
worm farmers from culturing them on ‘recipes’ of different organic wastes.
Before long growers realised that they could make money by selling a few
earthworms and a ‘growers’ manual’ to others at a high initial price, with
a promise to buy back all earthworms reared (at a much lower price). These
were then sold to others interested in the scheme. This practice, a classic
example of pyramid selling, earned earthworm culture a bad reputation. At
the State University of New York, Roy Hartenstein and his colleagues have
done much to rescue the idea, however.

In 1975, the authorities in New York banned the dumping of municipal
waste at sea, precipitating a crisis in the city. Hartenstein thought earthworms
might be able to help. At any sewage works millions of earthworms live in
trickling filter beds and treated sewage sludge, helping to break it down.
If earthworms lived naturally in sewage treatment plants, perhaps they could
be used in a more positive manner to deal with waste, Hartenstein reasoned.
His idea was to culture earthworms on sewage sludge, which they would convert
to an odour-free, nontoxic material. Researchers at the university found
that, under certain conditions, E. fetida grew and reproduced prodigiously
in sewage sludge. Harmful microorganisms, including Salmonella, were killed
during their passage through the earthworm’s gut.

But experimental cultures in the laboratory are a far cry from the millions
of tonnes of sewage sludge American cities produce each week. Several waste
treatment works across the US set up pilot schemes. The two largest were
at Lufkin in Texas, and Keysville, Maryland. The Lufkin plant could process
between 3 and 4 tonnes of sludge a week, by spraying thickened sludge over
outdoor beds of sawdust to create a material suitable for vermiculture.
At Keysville, the technique was different, involving raised indoor beds
and concentrated air-dried sludges. The techniques turned out to be uneconomic.
Other problems dogged the scheme: although the worm-worked sewage sludge
would make an excellent compost, it carries the taint of a product of human
sewage – the possibility of carrying pathogens and heavy metals.

Even the failure of worms as sewage workers did not put an end to vermiculture,
however. Clive Edwards of Rothamsted Experimental Station, in Hertfordshire,
took up the idea. Edwards understood the almost insurmountable difficulties
in using earthworms to deal with human waste, but saw that the idea could
be adopted to work with animal wastes far more easily.

Modern, intensive animal husbandry has produced a huge problem in disposal
of animal excrement. Most farmers see the waste as something that must be
got rid of as quickly and as cheaply as possible, without thought for its
potential value. Edwards and his colleagues at Rothamsted showed that earthworms,
especially E. fetida, grew as well in waste from cattle, pigs and horses
as in human sewage sludge. They even grew in the vegetable waste from the
potato processing industry and the paper making industry. Earthworms could
also break down the contents of the guts of slaughtered animals. They were
versatile indeed.

The researchers at Rothamsted continued to experiment to find the conditions
under which worms grew best. They also looked at the potential of other
species of earthworm. The next step was to scale up from the laboratory
bench to the farm. The large-scale system involved polythene tunnels containing
sophisticated worm-beds, with drainage, under-floor heating, sprinkler systems
and machinery that placed a thin, even layer of waste onto the beds at regular
intervals, allowing the earthworms to move up through the waste as they
processed it. Also, most importantly, an earthworm separator was designed,
to remove the earthworms from the processed waste.

At this stage, economists at the Agricultural and Food Research Council’s
Institute of Engineering Research at Silsoe, Bedfordshire, came to an interesting
conclusion; that the processed waste material had the greatest added value
as a horticultural growing medium, and the earthworms themselves were not
significant. Directives from the European Commission on protein production
from novel sources would have made it almost impossible to sell earthworms
as food to manufacturers of animal feed. The economic report changed the
direction of research towards making the best use of ‘vermicompost’. In
1983, British Earthworm Technology acquired a licence to commercialise the
work at Rothamsted and began the task of marketing a worm compost, derived
from animal waste, as a horticultural product.

Unlike material derived from sewage sludge there are no problems with
heavy metals (except in the case of pig slurry, which sometimes contains
high concentrations of copper which is fed to pigs to promote growth). However,
most commercial composts are based on peat, with nutrients added to make
up the final material. The range of nutrients and the concentrations in
which they are present vary enormously in animal wastes, depending, for
example, on the animal’s diet and how the waste was stored. This is a major
obstacle in preparing a commercial worm compost. It is cheaper to start
with inert peat and add nutrients as necessary, than to start with a material
that must be analysed to measure the concentrations of nutrients, and then
adjust them accordingly. Adjustments are most difficult when elements are
present in excessive concentrations, when they must be diluted. For example,
farm animals excrete high concentrations of potassium ions. ‘Vermicompost’
could be marketed simply for its organic matter, as a mulch for example,
but this would reduce its added value. A key advantage of composts derived
from worms is that the material is completely ‘organic’, which can be used
as a marketing ploy.

British Earthworm Technology had to make other commercial decisions.
Should it set up several regional centres to process waste brought in from
local farms, or should farmers be encouraged to set up their own worm-processing
facilities, selling the compost under a common brand name? The company faced
another, fundamental problem in trying to sell the system to farmers. Most
animal waste comes in one of two forms: as a liquid slurry, or mixed with
bedding material to form the traditional farmyard manure. To process slurry,
a farmer needs a slurry-separating machine, a sort of sophisticated mangle,
that produces a liquid that can be pumped and a solid that earthworms can
get ‘stuck into’. Such equipment is expensive and few farmers invested in
it. Ordinary farmyard manure does not need any treatment before cultivating
worms in it. The end product contains pieces of straw that the earthworms
cannot break down. This does not make the material any less useful for growing
plants in, but in a market where the look, smell and feel of a compost are
all important, lumps of straw lower its value.

Just as earthworm culture was gaining some commercial credence, the
Agricultural and Food Research Council withdrew its funding from the core
research, arguing that the work could now stand on its own. The company
still needed basic research to test and develop its products, however. Moreover,
worm culture was never meant to be simply a commercial exercise. Any process
that dealt effectively with the ever increasing quantities of farm waste
would also help to ease problems of pollution and odour.

The withdrawal of funds was disastrous. The company had several products
to sell, mainly to gardeners under the brand name ‘Betagro’, but a series
of poor summers led to poor sales of gardening products. Despite attempts
to secure financial backing for the company, British Earthworm Technology
finally became mankrupt last year.

Not everyone gave up on earthworms, however. Several companies operate
on a small scale, selling compost to local markets as a speciality product.
These include Turning Worms in Aberystwyth, Wonder Worm in Yorkshire, Biological
Resource Technology in Kent and Comprostein in Humberside. Ray Shaw of Comprostein
claims to have developed a new scheme to turn pig slurry into compost using
species of earthworm from the Far East and yeast. Whether any of these companies
succeeds remains to be seen.

Many toxic pollutants released into the environment eventually end up
in the soil. Because earthworms are in such intimate contact with the soil
and pass huge quantities through their guts, pollutants affect them more
than any other animals. This makes them potentially good biological indicators
of pollution. An international research programme is testing how effective
they are as indicators for pesticide residues, polychlorinated biphenyls
(PCBs), heavy metals and radionuclides.

An assay of earthworms can take one of two forms. The first involves
analyses of the worm’s body tissues to measure the concentrations of pollutants.
The alternative, where the toxicity of a pollutant is known, is to measure
the decrease in the size of populations. The European Commission and the
OECD have put forward the earthworm E. fetida as a good indicator of toxicity
in the environment. This requires the development of sensitive, reproducible
techniques that are cheaper than conventional chemical analysis. In nature
so many interacting factors influence the effects of pollutants on earthworms,
that much more work is still required.

The worm has come a long way since Darwin’s day. Yet still it is not
fully appreciated. Like the worms themselves, much of the animal’s biology
remains hidden. As biologists understand more about the ecology of earthworms,
and learn from past failures, the chances of putting worms to work on a
large scale grow more promising.

* * *

Cashing in on the lifestyle of an earthworm

EARTHWORMS show three distinct ‘lifestyles’. First are the large, deep-burrowing
types, such as Lumbricus terrestris. L. terrestris comes to the surface
to feed, dragging food, such as leaves, down into its permanent burrow.
Second are the smaller burrowing species, such as Allolobophora chlorotica,
the green worm. These earthworms do not burrow so deeply into the soil,
and feed on small particles of organic matter and microbes within the soil
matrix, which they obtain by ingesting large quantities of soil. Finally,
there are deeply pigmented earthworms such as the redworm, Lumbricus rubellus,
which feed on the surface. These worms are in greater danger from freezing,
drying and predation, but they benefit from a food rich in organic matter.
This is the type of earthworm that can be exploited in vermiculture.

Earthworms that live in the soil improve it in several ways. They drag
organic matter from the surface and mix it with mineral soil, preventing
the development of mats of organic matter. Their feeding activity releases
nutrients locked in such material and makes them available to plants. The
burrows of soil dwelling earthworms help to aerate the soil. More important,
they improve infiltration of water from the surface of the soil, preventing
waterlogging and compaction. The intimate mixing of organic matter, microbes,
mineral soil and secretions from the worm’s skin and the gut all contribute
to the formation of stable soil aggregates, producing the crumbly texture
of a fertile soil.

In the treatment of organic waste, surface-feeding earthworms function
as a shredding machine, breaking up large lumps of material as they ingest
it, mixing the material and increasing the surface area to allow better
aeration and drying. This, in turn, stimulates the activity of decomposing
microorganisms. The earthworm’s gut is a stable environment to encourage
the activity of beneficial microbes. The end result is a fine, stable, odour-free
material, containing most of the nutrients from the original waste.

David Knight is in the department of biological sciences of the University
of Exeter.