David North, Head of People and Wildlife
He thought of all the infinitesimal
motions of the world, the obstinate, heartbreaking progress of an earthworm,
eating its own route forward.
(Carrie Brown, Rose’s Garden)
The power of earthworms comes not from
their individual strength but from their collective strength – something we in the
conservation movement could perhaps learn from!
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| Earthworm, photo by Richard Burkmarr |
Out of sight
and out of mind. In your garden, in the fields and woods of Norfolk, and across
Britain, from our Cley Marshes reserve on the Norfolk coast to the Cors Dyfi nature reserve on the Welsh
coast (run by Montgomeryshire Wildlife Trust), uncountable numbers of worms are
doing what worms do best, eating and tunnelling, and in the process building
our Living Landscapes.
How often do
we wonder about what lives under our feet – the life in the soil. Millions – no
billions - of living creatures inhabit every garden, living their lives unnoticed
in the soil. None are more important than earthworms. There are worlds within
worlds under our feet – soil is a habitat that supports a myriad life forms,
from the microscopic to the massive, including the earthworms most feared
enemy, the mole. (A species for a later post perhaps!)
Worms are blind,
deaf, have no spine, no bones, no teeth, a length of just a few inches and
their bodies are 80% water. So why include them in my list of 100 species that
make Norfolk?
Well Charles
Darwin said of the earthworm, ‘It may be
doubted whether there are many other animals which have played so important a
part in the history of the world, as have these lowly organised creatures.’ The
power of earthworms of course comes not from their individual strength but from
their collective impact – something it took the genius of Darwin to recognise.
Charles
Darwin, one of my naturalist heroes, was the first person to take earthworms
seriously. Though perhaps seriously is the wrong term, as his research included
getting his wife to spend many hours singing and playing music to worms to discover
if they could hear! However from his observations of worms Darwin drew
remarkable and profound conclusions. This interest in earthworms was encouraged
by an observation made by his uncle Josiah Wedgewood (of Wedgewood pottery
fame) who observed that pieces of brick he had spread in a field had slowly
become buried. Darwin immediately thought from his studies that earthworms were
a likely cause.
His great
insight was to realise that the small changes made by the individual earthworms
he observed , when multiplied by billions for all the worms in England, and
across thousands of years, could bring ‘geological’ scale change.
As he
modestly records, 'The subject may
appear an insignificant one but we shall see it possesses some interest’. The
results of his 35 years of observations on earthworms were published in his
final book, ‘The Formation of Vegetable
Mould, Through the Action of Worms, With Observations on Their Habits’
published in 1881. A book which surprisingly sold more copies in its first year
of publication than ‘Origin of the Species’ achieved!
So how are
earthworms landscape builders? Darwin estimated that an acre of grassland might
support 50,000 worms and that the weight of their casts (posh term for
earthworm poo) would amount to 18 tons a year. We now know that Darwin’s
estimates were on the low side – indeed if you count worms of all species then
an acre of good land could support perhaps a million worms!
To understand
the importance of earthworm poo, sorry casts, it’s necessary to know a little
about their lifestyle. Earthworms are a bit like archaeological JCB diggers. They
tunnel through the soil, eating as they travel, passing the earth through their
muscular guts and rising to the soil surface to leave their casts. In this way
Darwin estimated they increase the depth of the soil by 0.2 of an inch each
year. That might not sound much but try multiplying it up through time! In ten
years an object on the soil surface will be buried 2 inches deep and after
1,000 years by 200 inches. So Darwin had cracked Josiah Wedgewood’s puzzle of
his vanishing bricks. Earthworms are great survivors. Worms (though not our lumbricus terristris) have been around
for at least 500 million years and survived at least five great extinction
events.
But worms of
course provide far greater services to us than gently burying former cities and
civilizations for today’s archaeologists to unearth. Earthworms have been
described as ecosystem engineers. They change the structure of their
environments. Their burrows allow both air and water to penetrate soils but
also help prevent water-logging. It’s estimated the tunnelling or worms each
year on an acre of grassland creates a drainage system equivalent to installing
2,000 feet of 6 inch pipe!
Darwin
described earthworms as nature’s ploughs, 'The plough is one of the most ancient and most valuable of man’s
inventions; but long before he existed the land was in fact regularly ploughed,
and still continues to be thus ploughed by earth-worms.’ Darwin.
Earthworms, including Lumbricus terrestris, by the way they feed, are very effective
at increasing the organic matter in the soil. They pull leaves and decaying vegetation
from the soil surface down into the soil. This method of feeding releases the
nutrients locked up in dead plants, making it available to living plants. As
they tunnel and feed they break dead organic matter into tiny crumbs with a
large surface area that bacteria and fungi can then break down releasing plant
nutrients.
Darwin’s
observations on the importance of earthworms have more than been confirmed by
scientists today. Indeed we are still discovering new benefits that earth worms
provide. Recent studies have shown that worm casts contain strange structures
of calcium carbonate but in the form of amorphous calcium carbonate which is a
very strange and special structure. A single earthworm may produce between 0.2
and 4.3 milligrams of calcite a day. That doesn’t sound much but earth worm
produced calcite could lock up 564kg of carbon per hectare per year. That’s as
much carbon as would be locked up by tree growth if a hectare was planted up. Pretty
amazing. Maybe it’s the earthworm that holds the answer to climate change. Its
already busy working to protect us from sea level rise of course by raising the
land surface.
It has even
been suggested that the origins of human civilization and farming can be linked
to earthworms. For the last 11,000 years of human history, ever since we first
became farmers, people have benefited from earthworms tilling the soil and
providing nutrients to our crops. It may be no coincidence that the first great
civilizations, first cities, and perhaps even the invention of agriculture,
occurred in areas rich in earth worms. The Nile, Indus and Eurphrates valleys,
where our first great civilizations prospered, were exceptionally rich in
earthworms. Earthworms in the Nile Valley have been shown to deposit up to a
thousand tons of castings per acre per year, explaining the astonishing
fertility of the valley. The rise and fall of civilizations may be as strongly
linked to soil fertility as it is to emperors and kings, or human wars and
battling philosophies. As Andre Voisin suggested, ‘One often reads of the thousands of slaves that built the Pyramids of
the Pharaoh. In actual fact, these enormous edifices owe their existence in the
main to the thousands of slaves inhabiting the sub-soil of Egypt.’ (Andre
Voisin Better Grassland Sward 1960)
Darwin may
not have used the term ecosystem service but he certainly discovered, and
understood, the principle that people benefit from nature’s services. His
pioneering studies on earthworms are still to my mind the best on an ecosystem
service. He recognised the great truth about soil, which he refers to as
vegetable mould, ‘‘All the vegetable
mould over the whole country has passed many times through, and will again pass
many times through, the intestinal canals of worms.’ (Darwin).
Of course its
not just people who benefit from earthworms. They are vital in the food chains
of many other species. And it’s not just early birds that catch the worms, a
whole host of wildlife, from shrews and voles to moles and badgers, rely on
earthworms in their diets. This key role in food chains was understood by
another great natural observer, Rachel Carson. She also recognised that worms
ingesting soil would mop up and concentrate in their bodies chemical poisons
such as DDT being used by farmers. She found that worms were able to take up
huge quantities of persistent DDT from the soil without it killing them, but a
small bird would be killed, or rendered infertile, by eating just 11 worms. Her
studies led to the publication of Silent Spring in 1962, A book which did
change the world and eventually led to the banning of these poisons. Even more
recently it’s been shown that other poisons, such as PCBs, are broken down much
faster in soils with healthy worm populations. Today worms are used both for
pollution control and waste disposal.
So next time
you stand in your Norfolk garden, or walk through a Norfolk wood or meadow,
think about the worms under your feet. There is a whole world down there in the
soil – a world as full of mysteries, dramas and magic; of predators and prey,
food-chains and habitats, parasites and symbiants, as in our world. The hidden
depths under our feet are as strange and biodiverse as any of the ecosystems in
the superficial world of the surface. I wonder, when we own a nature reserve how
deep does our ownership go? Do we own the world up to a metre down? 10 metres? 100
metres? Life penetrates deep – is that life part of our nature reserves?
I don’t have
an answer to that question, but I do know, if I had to choose one species that
puts the life in our Living Landscapes, it would be the earthworm. They were
once known as ‘angels of the soil’. That seems a pretty good name to me too.
‘I would not enter on my list of friends the
man who needlessly sets foot upon a worm.’ (William Cowper)
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