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