The Metropolis in the Woods | Northern Hairy Wood Ants

ROSIE HOLDSWORTH There's one there, there's a little one

there, there's another big one down there. Once you start getting your eye in, you notice there are like tiny little tracks and paths that are kind of clearer areas on the forest floor and it's like an ant motorway. Millions of workers, a network of busy roads, shared resources and a strong tradition of looking after your neighbours.

The make-up of any northern community. But this one might not be quite what you'd expect. We're in the woods at Hardcastle Crags, just outside Hebden Bridge, and today we're heading down to the forest floor to meet one of the North's most special and unusual communities. I'm Rosie Holdsworth, and you're listening to Wild Tales. The Metropolis in the Woods.

Hidden away in a steep-sided valley deep in the Pennine Hills of West Yorkshire is a secret society that outsiders are only just beginning to understand. It's a radical, female-led, workers' cooperative commune of hairy-faced, friendly northerners, which exists in perfect harmony with its woodland neighbours and is entirely solar-powered.

And where has this utopian vision been realised, I hear you ask? Hebden Bridge, of course - my hometown. Variously reported to be one of the funkiest towns in the world, the lesbian capital of the UK and the greatest town in Europe. Hebden and the wider Calder Valley has a rich history of doing things differently. But the secret society I'm proud to introduce you to today aren't the valley's bohemian human residents. They're the Northern hairy wood ants and they're even more strange and interesting than the regulars at The Fox and Goose.

Come with me and find out more. We'll start seeing ants, eyes peeled. Yep, there it is. Once you get your eye in, you start seeing them all over the show. These are incredibly special ants. I mean, all ants are special in their own way, but these ones are a particular favourite of mine because they are Northern hairy wood ants. So the northern bit is they live at quite high latitudes. There's big populations of them in the Highlands of Scotland.

Actually, where we are here, we're towards the southern edge of their range. They're hairy, and this is my favourite thing about them. They're hairy because they've got hairy eyebrows. When you look at them under a microscope - and I can confirm because I have done this - they do have a hairy little face. So, there's lots of different wood ant species but these ones are special to the north, and that means that they're friendly hairy northerners! And what's not to love about that?

So, we're in a mixed area of woodland here, so we've got some deciduous trees, some coniferous trees, there's quite a lot of light coming through the canopy, and then this area here, we've got nice big open space and several enormous anthills. So the anthill is a metre and a half wide, about half a metre tall, and it's made up of a real mixture of pine needles. They're quite good construction materials, because you can kind of knit them together like a bit of a thatched roof.

But there's all sorts of little bits of twigs and soil and bits of pine cone that the ants have used to construct this nest. Actually, although it just looks like a heap of sticks from the outside, inside there, they're really quite complex structures. With specific areas of the nest for specific things, so there's a nursery area in there, there's all the different connecting tunnels, there's the areas where the ants bring food, they store them in larders in there, there's a graveyard in there, which is pretty wild, where they put the dead ants, I guess, to make sure that disease is isolated from the rest of the colony.

And the whole nest is designed to maximise solar gain. So they're solar engineers as well as everything else. My favourite time of year to come and see the ants is really early spring, when we start to get slightly warmer days, the sun starts to shine, because over the winter a lot of the ants die off, the nests massively reduce in size and they're really no more than like a little bit of a bump on the forest floor. And then, late February, the ants start to emerge and they'll come up on the ground to the surface of the nest in a huge swarm. They can literally, like, carpet several meters squared, and they're basking in the sun, bringing that energy and that warmth back down into the nest to kind of

kick-start the nest building and that regeneration through the spring and summer. So, a mound like this, during the winter, will reduce probably by like three quarters, and then through the summer they'll build it back up again. On top of what looks like, just a big pile of sticks, that is, in fact, the ant nest. Actually, once you get your eye in, the whole thing, the whole structure is moving. And that's because the entire thing is covered in ants. There's hundreds of them up on the surface of the nest.

When you look closely at the top of the nest, there's several tiny little holes which are the kind of entrances into the nest, and they're coming in and out of those. Whoa, look at that one! So, it's a tiny ant, it's probably like two millimetres long, and it's got a set of pine needles that are probably 20 times its own length. They are absolutely amazing.

One of the reasons that the ants here at Harcastle Crags, the Northern hairy wood ants, are so special to me is that they're actually one of my first memories of the crags. So, I grew up around here, we used to come here loads when we were kids, and I've got really vivid memories of walking on the top path, which is a beautiful, ancient pack horse path with big gritstone flags. And all across that path, there are these ant motorways where the ants are crossing the path, and you can't help but encounter them. And I remember as a little kid finding it really, really hard walking up this big, steep path and just seeing these teeny tiny little motorways of great big ants, and they were walking faster than I was. And thinking, if a teeny

tiny little ant can manage to get it up the hill, I'm sure I can make it to the top. I've got very vivid memories of seeing the ants when I was little, and it's really nice to kind of close the loop and come back and be looking after the woodland on behalf of them now. In true Calder Valley fashion, it's started to absolutely bucket down, so we'll go and find somewhere a little bit drier and hopefully find a couple of our volunteers who can tell us a whole lot more about our fantastic ant friends.

We've been brave and come out to a different part of the woods to meet up with a couple of our fantastic volunteers, Anthony and Steve, who are going to tell us a little bit more of the detail and the background to the Northern hairy wood ants at Hardcastle Crags. Hiya both.

STEVE Hello.

Well, I'm Steve, who's a general naturalist really. My main interest at Hardcastle Crags is in the breeding birds.

ANTHONY I'm Anthony Arak, I have a background as a zoologist

and I'm very fond of insects, particularly moths, but also ants.

ROSIE HOLDSWORTH The nests that we see, the high mounds on the

ground, they're quite an obvious structure, but what's actually going on within there?

ANTHONY Well, somewhere down there in this mound, there is a

queen in her chamber, and she's the only ant that produces any eggs. Most of them running around on the surface are workers, but they're responsible for gathering the food to feed the grubs, but their lifespan is two or three months, whereas the queen may live 10 to 20 years. As its name suggests, it is a northern species distributed in Scotland down to Mid- Wales, North York Moors and the Derbyshire Dales. You don't find it in every piece of woodland and so that's why Hardcastle Crags is very special.

ROSIE HOLDSWORTH As you cast your eyes across the forest

floor you can see why.

ANTHONY There are several hundred nests that have been

recorded here, which equates to roughly between 3 million and possibly 60 million ants in total. So there's a lot more ants than there are people living in Calderdale.

ROSIE HOLDSWORTH And they're not all living in one enormous

ant city either. This metropolis is made up of lots of different neighbourhoods.

ANTHONY One of the most interesting things about this

ant species is that it's polydomous, in the sense that it has several mounds in each colony. Where we're standing now, we can see at least three different anthills, and they all belong to the same colony. And it's possible that there's a queen in each of these mounds. But at a certain time of the year, the workers will produce more queens by selectively feeding certain larvae better-quality food, and they will develop into queens, which then disperse with a small army of workers. And they may either fly or walk and the male with his wings will mate with the queen and then she'll establish a new colony close by.

So, it's possible that you might find a dozen ant hills which are all connected by little trails, and so they all belong to the same colony, but may have several queens.

ROSIE HOLDSWORTH So what does a queen Northern Hairy wood ant

look like?

ANTHONY The queen's quite a lot bigger than the other ants,

and she's the only one that lays the eggs, and she chooses whether to fertilise the eggs or not. So fertilised eggs turn out to be workers, some of which may be Queens. Unfertilised eggs turn out to be males, the drones, which fly and mate with the queen. So she has the ultimate control over deciding the ratio of drones to workers, and it's the workers that have the control, deciding when to produce another queen.

ROSIE HOLDSWORTH Ants are insects, when we talk about them

deciding things, it's quite difficult to grasp the concept.

ANTHONY It's an instinct, if you like, which is genetically

controlled. They are very social, and I suppose they're kind of like a model for a very cooperative human society at its best. And all the workers are sisters, so they all have an interest in each other, and they especially have an interest in protecting the Queen because she's the one that produces more sisters.

So it's a complicated genetic system. It creates that co-operation because all the ants in the colony are very close relatives.

ROSIE HOLDSWORTH Yeah, co-operative sisterhood,

female-led society. It's very Hebden Bridge But these ants aren't just interesting because of how they live. These spectacular nests play an important part of the woodland ecosystem.

ANTHONY The ants are an incredibly important keystone

species here, not only as food for birds but, because they consume a huge number of invertebrates on the forest floor they have a major impact on the invertebrate fauna.

ROSIE HOLDSWORTH Ants are quite voracious predators in terms of

some of the other invertebrate species in the woodland, but what eats them, Steve?

STEVE Well, the only bird that I definitely know eats them in

these woodlands is the green woodpecker, because I've seen them burrowing in, and throwing pine needles this way and that.

ROSIE HOLDSWORTH As well as providing a tasty snack for

green woodpeckers, ants can have a rather more unusual relationship with birds. In spring you might happen upon a bird tucking ants in between its feathers.

STEVE That's referred to as anting. And they look as if

they're in distress, they're flopping around on the ground with their wings open, and you see them pecking, and they're picking up ants and putting them under their wings. And apparently the ants kill off the pests that are on the birds.

ROSIE HOLDSWORTH They do this by spraying formic acid onto the

feathers. But they're not just providing unusual beauty treatments for birds, the ants have another purpose.

ANTHONY Very interestingly, they also climb trees.

They go right to the top of these tall, pine trees here to milk aphids. And these aphids are totally dependent on the ants for protection. And in return, they produce honeydew from their bottom, and the ants will milk the aphids like an aphid farm. And they'll come down with the honeydew and regurgitate it to the larvae in the colony.

Particularly favouring those that are destined to be queens in the future. So they have a complicated relationship with aphids at the top of trees.

ROSIE HOLDSWORTH This is what's known as a mutualistic,

symbiotic relationship, which means both species benefit from working together.

ANTHONY Last year, we were very lucky because there was a

small sapling pine tree growing next to a mound with aphids on it, and we actually managed to get some photographs of the ants milking the aphids and stroking them to encourage them to exude the honeydew, which was amazing.

ROSIE HOLDSWORTH But that relationship could be under

pressure too.

ANTHONY Because the aphids are very temperature sensitive, and

if it gets very hot, above 30 degrees, the aphids can die. So, with the warming climate, It's uncertain whether the Northern hairy wood ant will survive or whether it will be pushed further back north, where you have a colder season in the summer.

ROSIE HOLDSWORTH So, we may not know exactly where these ants

will be in the future. For the time being, they're doing well here at Hardcastle Crags. And keeping it that way means looking after the woodland they call home. The rain stopped. I've left Steve and Anthony because I got the final piece of the jigsaw in a different part of the woodland, and I'm going to go and meet some of the ranger team, and have a little bit of a chat about how we look after the woods and consider the ants. Here I am with Alice, and Tim, and Lily who's up the hill somewhere.

Hello.

ALICE Hello.

I'm Alice, I am the area ranger here at Hardcastle Crags. This bit of the woodland that we're in is what's known as plantation on an ancient woodland site. So there's loads and loads of larch trees and Corsican pine. We do have a few sort of specimen oak trees in and amongst the dense pine and larch.

What we're doing today is marking up some trees to fell this year. Every time we're out felling, we do see the ants' nests, and we're working in and around them, so we're always very mindful of how our work could impact the ants. So we're really careful not to disturb the nests. If we find a nest, we'll sort of make each other aware. You quite often notice the ants going up and down a certain tree to collect materials for the nest, so we'll keep a good eye out for ants on the trees that we're marking up and make sure we don't touch them.

And then, obviously, in the actual felling process, once it's on the ground we actually extract quite a lot of the timber for firewood, which we use on site. But that does involve dragging the logs from the woodland to the trackside with a winch. So, we'll sort of walk the route that we're planning to take and just check that there's no ant activity in that area.

Last year, and hopefully this year, we're looking into using logging horses. With a machine and a cable you're pulling in a straight line and the horses can sort of weave their way round obstacles more easily. We cut down certain trees to open up more light, to make way for ants, because they like the light to come in, as well as to allow the ground floor to establish and, you know, promote natural regeneration of other trees. Creating a better age structure in the woodland, to create a more resilient woodland to things like disease and climate change

ROSIE HOLDSWORTH So, what's good for the woodland is good

for the ants and what's good for the ants is good for the woodland. So, as we leave Alice and the rangers to crack on with their work marking up in the woodland, I'm really struck by the similarities, actually, between the woodland work that we do as part of the ranger team here at the crags and the work that the ants are doing to keep those ant colonies up and running and healthy, keep the ant hills constructed and looking beautiful.

There's a teeny tiny little ant nest. So this is an area where we've done quite a lot of work in the last few years. So the light levels in here really have changed. We're starting to see some more of that ground flora, some more of the plants, little bilberries here, brambles, that kind of thing, starting to colonise this area because the light has increased.

And in a vote of confidence, the ants have also moved in. Thanks for listening to this episode of Wild Tales. If you've enjoyed it, why not give us a follow and a review? And if you'd like to know more about the Northern hairy wood ants at Hardcastle Crags, please head to the episode show notes. I'm Rosie Holdsworth. Goodbye.

The Metropolis in the Woods | Northern Hairy Wood Ants

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