You're listening to CowdScience from the BBC World Service, the show that drills down
into your questions about life, Earth and the universe. I'm Anand Jagatia and for this
episode, I've been doing a bit of DIY. In fact, I'm building a house for worms. This
consists of some plastic crates which I'm going to stack on top of each other. I've
drilled some holes in the crates for ventilation filled them with compost.
So what we got in here…
…smells disgusting.
Okay, so we got some bits of banana, bits of old bread, eggshells... And then, right
now I just need to add some worms.
Just gently spread you out.
This is kind of gross. I don't want to hurt them either.
There we go. just tuck them up. While I get accustomed to my new pets, let's hear from
this week's listener, to find out exactly why we're doing all of this.
My name is Dinesh and I'm from Tamil Nadu in southern India. I want to know how important
earthworms are for farmers.
How important are earthworms for farmers? Dinesh wants to know as he works on his parents’
farm in Tamil Nadu, which is where he spoke to us sitting underneath a tree with some
of their animals in the background.
Right now we have goat and rooster, parrots…
Parrot is a pet…
Do you grow things in the in the earth as well?
Yeah, our primary farming is rice.
Do you notice that in the earth where they're growing that there's a lot of lot of earthworms
in the ground?
Yeah, we actually grow earthworms separately. Keeping the soil alive.
Dinesh’s farm is organic. They use cow dung as fertiliser and not really much else. But
he says that's not the case for lots of other farms nearby.
The others use chemical fertilisers. So that's the main question for me. What happens if
you use chemical fertiliser in the field? What happens to the worms?
Dinesh is curious about how inorganic or organic farming practices can affect earthworms and
how earthworms can affect his farming. He's noticed that the earthworms he cultivates
and adds to the soil do make a difference to how well his crops grow. But how exactly
and why? Now, I must admit that before building this wormery, the last time I picked up a
worm was probably as a kid playing in the garden making mud pies. But even though we
don't really see them, beneath our feet, the Earth is teeming with these subterranean annelids.
And while they're not exactly glamorous, they have the power to engineer entire ecosystems,
as we'll hear later in the show. Now, when it comes to being fascinated by the humble
earthworm, Dinesh finds himself in some pretty excellent company. Back in 1881, none other
than the great Charles Darwin published his last scientific book, which was devoted to
the behaviour and ecology of earthworms.
I became interested in them and wished to learn how far they acted consciously and how
much mental power they displayed. I was the more desired to learn something on this head,
as few observations of this kind have been made, as far as I know, on animals so low
in the scale of organisation, and so poorly provided with sensory organs, as are earthworms.
Darwin devised all kinds of experiments to learn more about earthworms, including what
their favourite foods were, whether they could sense light and heat, and whether they could
respond to sound, which involved playing them the bassoon, shouting at them - No, really
- and placing pots of the poor things on top of a piano. It turns out that earthworms don't
have ears, but he discovered that they’re extremely sensitive to vibrations. Some of
these experiments lasted decades, and in fact, a few of them are being recreated today in
the grounds of the house where Darwin lived and worked.
Charles Darwin studied earthworms throughout his life. And specifically used Down House,
the estate there, as an outdoor laboratory.
This is Kevin Butt, head of the earthworm research group at the University of Central Lancashire.
Earthworms are sometimes referred to as Darwin's plough and this is because their natural activities
in the soil turn it over. They bring mineral soil up to the surface and they take organic
matter down into the soil to act as food for themselves. So in doing so they actually mix
the soil layers. And by passing the soil through their gut, they create a really good quality
crumb structure to the soil, which is great for growing plants in.
It’s quite a long walk to Kevin's other experiments.
Kevin wasn't able to meet us in person, but luckily we were shown around by Jane McLaughlin
who volunteers at Down House and also works as a research assistant on Kevin's worm experiments.
This is Kevin's experiment set out in the field, to look at what Darwin observed with
the sinking into the ground.
What are we looking for?
We're looking for big flints.
Darwin observed this effect in action at Bucklands Meadow. Over 30 years he documented the disappearance
of large flint stones, some according to his notes half as big as a child's head, as they
slowly became covered with earth. This, he believed, was due to the action of worms.
As Jane explained to me standing at the same spot today.
He observed originally a layer of ash sinking into the ground. But then he said, Well, why
do Roman pavements sink into the ground? Why do buildings, old buildings sink into the ground
and it's all because he postulated because of the action of worms. This field was full
of big flints, but 20 years later, without doing anything, you could ride a horse across
the field, and the horse wouldn't strike its feet against any of the flint. So somehow where had the flints gone? This is why
earthworms are called Darwin's plough, because they have as much effect on the soil as ploughing
it would.
It's difficult to think of earthworms, pink fleshy squishy things, as a force of nature.
But acting in large numbers over decades that's exactly what they are, as Darwin's experiments
recreated by Kevin and Jane are now showing.
Earthworms are considered to be ecosystem engineers because they change the very nature
of the material that they're living within.
Can you kind of talk me through how this actually works? So how that helps to improve the quality
of soil and how it changes the soil? The type of worms that live in organic matter, are
taking that very raw material, usually waste vegetable, plant material, and they're passing
it through their gut, and within their gut, there are microbes that act upon that material
plus their own digestive enzymes, and they change the nature of that material and make
it more available more usable by other organisms within the soil. But also they change it chemically
so that it becomes more available to other organisms. Horizontal burrowing worms, the
ones that live just below the soil surface are geophagus, they eat their way through
the soil. So what they're doing is utilising organic material that is found within the
soil that's been brought down into the soil, and then mixing it with the mineral soil,
actually creating a better physical and chemical structure to the soil that then is much more
available to plants.
And then what about the third category of worms, ones that live slightly deeper in the soil?
The deep burrowing earthworms provide lots
of ecosystem services in the soil, they produce what are called macro pores, large holes in
the soil, extending down a metre, perhaps down to three metres at a time. This allows
water to enter the soil. This allows air oxygen to enter the soil, and so improves the quality
of the plants that are living there. In addition, of course, as they feed, they gather organic
material from the soil surface, things like dead leaves, and they drag that down into
their burrows. And by doing so, they increase the fertility of the soil and make that material
available to the other types of earthworms the ones that live just below the soil surface.
So the fact that our listener Dinesh finds lots of earthworms in his paddy fields in
Tamil Nadu means that his soil is probably nice and healthy. Those incredible natural
engineers he's introducing on his farm are not only mixing up the soil, they're refining
and improving it making nutrients more available to the plants. But it's not just Dinesh that
this is relevant for, this is something that could potentially affect all of us.
Because crops need to feed the world and we are increasing in population. So we would
need more food. And if earthworms can increase this crop yields, so more crops, that will
be a very good thing.
This is Ingrid Lubbers from the University
of Wageningen in the Netherlands. She studied the potential impacts that earthworms could
have on food production.
We’ve looked into crop yields, so the market crop. But we've also looked at above ground
biomass, so that's the entire plant. They all increased about 20 to 25%.
Wow. Okay, so that's a pretty big increase. Actually, I'm quite surprised at how big of
an effect the worms can actually have. How exactly do you think that is happening? What
are some of the ways that they could be increasing the size and the output of the plants?
Yeah, scientifically, that's, of course a very interesting question. How do they do
it? Well, by being active in the soil, what they do is that they increase the availability
of nutrients for instance, nitrogen. Nitrogen is really essential for all living things,
but also for plants. So to increase the availability of nitrogen for plant uptake.
You might be wondering something here. Nitrogen makes up about 80% of the air in our atmosphere.
So why do plants need help from earthworms to get hold of it? Well, pure nitrogen in
the form of a gas is pretty inert and isn't much used to living things. It has to be converted
into other forms by bacteria, first into nutrients like ammonium and then into nitrates and nitrites.
It's this form of nitrogen that plants can make use of to grow. Earthworms seem to speed
up this process by their action in the soil, making more nitrogen available for the plants
to use. Although Ingrid says that this effect is more helpful for some crops than for others.
We found it to be more helpful for let's say, grain crops and pasture grasses, and less
helpful for legumes so peas for instance.
Our questioner Dinesh he lives in India, and
his farm is organic, and they don't really use any kind of, you know, artificial fertilisers.
But what does using large chemical fertilisers do to soil does it add nitrogen in the same
kind of way that earthworms do?
That's the thing. It doesn't. So if you use
inorganic fertilisers, which include nitrogen then it's already fertilised in a way that
plants can take it up immediately or very fast. So if you are an organic farmer and
you use organic fertilisers or you leave the crop residues out of your land, then the earthworms
they eat it, they mix it into the soil, and in this way, make the nitrogen available to
the plants. And that's a slower process. But also, the effect of earthworms is used to
a maximum really.
Artificial fertilisers are great for boosting plant growth quickly, but they can also cause
nitrogen pollution when they leach into water systems, disrupting natural ecosystems and
they can make soil less healthy in the long run. Using earthworms to help fertilise soil
is slower, but they can boost yields by up to 25 percent, and they have the greatest
effect when the nitrogen availability is already low. So they could help organic farmers like
Dinesh to increase crop yields in the absence of artificial fertilisers while being kinder
to the environment. But it doesn't stop there. In fact, if farmers leave their crop residues
on their fields after harvesting, the earthworms can actually help to lock up carbon in the
soil.
It's said that earthworms can store carbon in the soil and they are supposed to be able
to do this by just feeding themselves with litter and mixing this litter. So, I mean,
that's plant remains, they mix that with mineral particles in the soil and excrete that as
their cast - so earthworm poo, and within these casts, the carbon is less available
for microbial decomposition, which would mean in the end that there's less co2 coming out
of the soil.
You're listening to CrowdScience from the BBC World Service, where this week we're looking
at how worms affect our soils - thanks to a question from Dinesh in India. Dinesh wants
to know how worms can help him to grow crops on his farm. And I'm also trying to harness
them here in my garden. It's been a few weeks since I set up my wormery with some worms
I was sent in the post. And I have to say, I am totally over my initial sense of slight
disgust. I'm looking at them now and they are basically amazing. I've been feeding them
bits of kitchen scraps over the past couple of weeks, and they are slowly but surely turning
it into a really rich, nice compost. Earthworms are like a small army of underground workers
that engineer the soil, aerating it helping it to drain increasing the availability of
nitrogen for crops and locking away carbon preventing it from entering the atmosphere
as a harmful greenhouse gas. It kind of sounds like it's too good to be true. Right? Well,
unfortunately, it is. This is the point in our story where we find out that the worm
has turned.
Worms do have lots of amazingly positive effects on ecosystems, but they have
some negative ones too. It's something that scientists like Ingrid called the earthworm
dilemma.
We have just discussed the upside that they are good for crop yields, so their activities
in the soil increased nitrogen availability, but the same mechanism can increase greenhouse
gas emissions.
So while earthworms can help store carbon
in the soil by locking up with minerals in their poo, they can also indirectly increase
the release of greenhouse gases. One of these is nitrous oxide, which is produced naturally
in the soil by certain microbes. But it turns out the earthworms just by going about their
business can rapidly accelerate this process.
Yeah, so the microbes produce nitrous oxides in the soil. And the earthworms are working
the soil, they're moving about into soil and while they do that, they dig their burrows
and make the soil more porous. And these pores, they can function as a little chimney. And
through these little chimneys, nitrous oxide gas can leave the soil from deeper in the
soil towards the atmosphere.
The role that earthworms play in greenhouse
gas emissions is complex. It turns out their activity may simultaneously increase and decrease
carbon dioxide or nitrous oxide. So Ingrid wanted to know when you tally it all up, which
of these effects wins out in the end?
If you look at the main effects, we found nitrous oxide emissions can be increased by
42%. So quite a lot. CO2 emissions can be increased by 33%.
Wow. Okay. So this is compared to soils where there are no earthworms.
Exactly.
Yeah. So we found these quite big main effects. But what I would need to add to that is that
most of these studies for highly manipulated laboratory studies so that means no plants
growing and also the experimental maturation of these studies. Yeah, 30 days, 100 days,
but not very long.
Okay, how do you think the figures would be different if you were able to study them in
a sort of real world situation? I mean, would it be that the worms cause a release of more
co2 from the soil, but because they're also stimulating plant growth and the plants will
capture some of that co2 and then relock it back into the soil?
Yeah, that's exactly the right question to ask because in real life, so not in the laboratory,
but out in the fields, you will have plants growing. So nitrogen will be taken up by the
plants roots, nitrogen can leave the system by leaching and less will be available for
the formation of nitrous oxide emissions, for instance.
In terms of overall global warming, then, how much do you think that earthworms, if
you did take these figures as being what's emitted by them, would contribute towards
global warming compared to other processes that happening on the planet?
You can make a very, very rough estimate, really a guess, you could say that perhaps
a maximum of 1% of global warming could be attributed to the activities of earthworms.
So it seems even though earthworms have a positive effect on soil fertility, which is
surely good news, this same mechanism could lead to an overall increase in greenhouse
gas emissions, which isn't such good news. It is worth pointing out though, that even
Ingrid's worst case scenario is still a tiny fraction of manmade greenhouse gas emissions.
Still, it's kind of hard not to marvel at the ability of the lowly earthworm to engineer
the soil under our feet and the atmosphere above our heads. The fact that they can increase
emissions from soil by 30 or 40% just shows how important they are for the processes on
this planet. I'm discovering pretty fast that you underestimate the power of earthworms
at your peril. And there are places on earth where scientists are realising just how true
that is.
I'm Erin Cameron and I work in the boreal forests in Canada, but it's actually a biome
that stretches across the northern part of the world. And they're basically forests that
are partly deciduous, like broadleaf trees and coniferous trees. And there's a thick
leaf litter layer on the forest floor, which is important for the research I do.
This layer of leaves on the bottom of these boreal forests - what's it like?
It's maybe five centimeters, or even 10, of fairly undecomposed leaves. Leaves that have
fallen in previous years take quite a number of years to decompose in those forests.
And why is that important?
A lot of carbon is stored there and a lot of animals live in that layer, like insects
and also things like salamanders or the plants have seeds that germinate in those layers.
For thousands of years, those leaf layers have been largely undisturbed, storing carbon
allowing new seeds to germinate and providing a habitat for a whole range of wild animals.
But not for earthworms.
Earthworms were wiped out of Canada and the northern U.S. about 10,000 years ago in the
last glaciation. But they've arrived since then, with European settlers. What they do
when they arrive in these forests is eat the leaf litter layer and that has effects on
the organisms that rely on that layer for habitat.
Erin and her team from St. Mary's University in Halifax, Canada, wanted to know what their
reappearance might mean for all that carbon stored in the leaf litter. And since there's
not much data available, they came up with a computer model to predict the possible effects
of earthworm activity on this unique habitat.
And what we found was that the carbon in the forest floor is reduced by about 50 to 94
percent 125 years after earthworms have invaded in the model. But most of that change occurs
35 to 40 years after invasion. And we tried to look at what these effects would look like
in a specific forest management region that's about 5.9 million hectares in size, and the
model predicted that forests for carbon stocks in invaded stands would decrease by about
2.7 million mega grams by 2056. That's about the same as 800,000 passenger vehicles.
If the simulation is correct, that's a whole load of carbon which normally sits on the
forest floor, which is going to be eaten by earthworms and released a co2 into the atmosphere.
Now, this is just a model so there are caveats. For example, they only looked at earthworms
that live on the top of the soil. These are the most common in northern Canada at the
moment. It's not yet clear what kind of effect deep burrowing earthworms may be having if
they also made far north. They may actually store carbon and counter the effect. But the
actual figure may be even higher, depending on whether or not the worms spread to more
of the forest than predicted. And it's not just in Canada that earthworms are colonising
the soil. They're spreading further and further north to colder and colder climates, which
could have serious consequences for Arctic ecosystems.
The landscape is kind of mountainous. So you have valleys where there's a little bit of
tree growth. So there's some forest but then as soon as you go up a little bit, you're
in landscape dominated by really small plants and the temperatures are around zero degrees.
So we're kind of at the border of Arctic conditions.
Welcome to the tundra of northern Sweden, huge treeless expanses where the temperatures
are freezing and the winters are dark for months at a time. It's a wild place home to
things like reindeer and arctic fox. But as ecologist Gesche Blume-Werry explains, it's
not somewhere you'd necessarily expect to find earthworms.
The idea with the earthworms really is that because it is quite cold that they might be
limited by the temperatures, because they are quite slow in spreading themselves, they
haven't really reached the upper northern limit of where they could be.
So they haven't got as far as they might be able to, but they have sort of started to
push up a little bit.
Exactly, yes, and the big thing really is that we humans often help them to get places
where they haven't been before and so we, you know, make these introduction points from
where and they can spread out. One of the classic examples is having worms as fishing
bait, going fishing and then maybe not using all the worms and then just emptying the can
afterwards. But also gardening – so, you know, if people buy soil that comes from elsewhere,
or have a compost or just also increased human activity in general, so it can also be completely
unintentional spreading.
The fact that earthworms are appearing in Arctic soils is worrying because it means
they could start to disrupt processes on a global scale. We heard earlier from Ingrid
Lubbers that earthworms are great for crop yields. They increase nitrogen availability
and allow plants to grow bigger and faster. But in the Arctic tundra where temperatures
hover around freezing for much of the year, nitrogen levels stay low, and so do the plants,
which is why there are no trees in this region. So when one of Gesche’s Master students
discovered earthworms here, she knew it was significant.
We measured a few different parameters that relate to productivity, the greenness of the
vegetation, we measured root growth and we also measured the height of some of the plants.
And then we also measured just kind of how much nitrogen they have in their leaves. And
we saw big increases in productivity both above and below ground and also quite strong
increases in nitrogen content underneath. It sounds ridiculous but we looked at like
the casts of earthworms - so the earthworm poop - and checked the nitrogen concentrations
in there compared to the normal soil in the tundra. And the nitrogen concentrations were,
I think more than 10,000% higher. And that was also a magnitude higher than the increases
that we see in agricultural side. So it seems that the tundra is also responding much more
than other soils.
And so I guess the reason why this is important is that in industries like agriculture, we
think of having more nitrogen available to plants as a good thing, because it means that
we can, you know, get more crops. It means our soil is more productive. But this kind
of mechanism could be a problem in Arctic ecosystems.
Yeah. So one problem that we see or one potential problem is that just if plants grow higher,
they might actually no longer be under the snow during the winter. So usually in Arctic
tundra, we have a lot of persistent snow cover where we don't see the plants and that means
that a lot of the incoming light is reflected. So everybody knows that white surfaces don't
heat up as much as black surfaces do. And one reason why that can be problematic is
that if you have less white surface or you have for example, shrubs or also grasses sticking
out of the snow, more of the light will be kept or more warming in the atmosphere.
Gesche and Erin, who works on the boreal forests in Canada, both agree that once worm arrive
in an area, it's basically impossible to remove them. Earthworms really are a kind of unstoppable
entity once they get going. We need them to help engineer our soils, and they could help
us to grow more crops with a smaller environmental footprint. But worms aren’t just vital for
our soils. They have implications for our entire planet. So I suppose it's fitting really
that we call them earthworms. Speaking of which, I've got to go and feed mine. For now,
I'll hand back over to listener Dinesh for the credits.
That's the end of this edition of CrowdScience from BBC World Service. Today's question was
from me, Dinesh Kumar in India. The show was presented by Anand Jagatia and produced by
Marijke Peters. If you have a question for the team, please email them at crowdscience.bbc.co.uk.
Thanks.