In Our Time - Pollination

Episode Date: April 3, 2025

Since plants have to mate and produce offspring while rooted to the spot, they have to be pollinated – by wind, water, or animals – most commonly insects. They use a surprising array of tricks to attract pollinators: striking colours, iridescent light effects, and enticing scents, to name but a few. Insects, on the other hand, do not seek to pollinate plants – they are looking for food; so plants make sure it’s worth their while. Insects are also remarkably sophisticated in their ability to find, recognise and find their way inside flowers. So pollination has evolved as a complex dance between plants and pollinators that is essential for life on earth to continue. With Beverley Glover, Director of the Cambridge University Botanic GardenJane Memmott, Professor of Ecology at the University of BristolAndLars Chittka, Professor of Sensory and Behavioural Ecology at Queen Mary, University of London.Producer: Eliane GlaserReading list:Stephen L Buchmann and Gary Paul Nabhan, The Forgotten Pollinators (Island Press, 1997)Lars Chittka, The Mind of a Bee (Princeton University Press, 2023)Steven Falk, Field Guide to the Bees of Britain and Ireland (British Wildlife Publishing, 2015)Francis S. Gilbert (illustrated by Steven J. Falk), Hoverflies: Naturalists' Handbooks vol. 5 (Pelagic Publishing, 2015)Dave Goulson, A Sting in the Tale: My Adventures with Bumblebees (Vintage, 2014)Edwige Moyroud and Beverley J. Glover, ‘The evolution of diverse floral morphologies’ (Current Biology vol 11, 2017)Jeff Ollerton, Birds and Flowers: An Intimate 50 Million Year Relationship (Pelagic Publishing, 2024) Alan E. Stubbs and Steven J. Falk, British Hoverflies (‎British Entomological & Natural History Society, 2002)Timothy Walker, Pollination: The Enduring Relationship Between Plant and Pollinator (Princeton University Press, 2020)In Our Time is a BBC Studios Audio Production

BBC Sounds, music, radio, podcasts. This is in our time from BBC Radio 4, and this is one of more than a thousand episodes you can find on BBC Sounds and on our website. If you scroll down the page for this edition, you can find a reading list to go with it. I hope you enjoy the programme. Hello, since plants have to find a mate and produce offspring

while rooted to the spot, they have to be pollinated by wind, water or animals, most commonly by insects. So they use a remarkable array of tricks to attract pollinators, startling colours, iridescent light effects, and enticing scents, to name it a few. Insects, on the other hands, do not seek to pollinate plants. They're looking for food, so plants make sure it's worth their while. Insects are also remarkably sophisticated in their ability to locate,

recognise and find their way inside flowers. So pollination has evolved into a complex partnership, a dance between plants, and pollinators that is essential for life on earth to continue. With me to discuss pollination are Jane Mamet, Professor of Ecology at the University of Bristol, Lars Chitka, Professor of Sensory and Behavioural Ecology at Queen Mary, University of London, and Beverly Glover, Director of the Cambridge University Botanic Garden.

Beverly Glover, can you tell her this as what pollination is and how it works? Yes, of course. As you said, it's the process by which plants go about sexual reproduction, And we're talking here about most of the plants that you'd imagine, oak trees, cabbages, rose bushes. There are a few that do things differently, mosses and ferns, but the vast majority of plants that listeners would think of need to use pollination for reproduction. And the reason for that is that just like animals, plants produce sex cells, so male sex cells, sperm cells and female sex cells, egg cells. But unlike animals, they can't move around to transfer those between individuals. And so what plants do is they take their male sex cells, the sperm cells,

and they package them up into a pollen grain. So it's coated in a coating that's water-resistant and decay-resistant, can survive out there in the environment. And then they have to transport that pollen grain to another plant where the sperm can fertilise the egg cell. Now they do that by releasing... Just a second. How big are these pollen grains?

How many pollen grains are there in one, as it were, voyage? It depends. So if they travel in the wind, They can travel singly. Some plants like orchids package up thousands of them together into a big ball of pollen that you can see easily as a chunky thing. The pollen grain itself contains only usually about three cells, so the sperm cell and another cell or two.

And what happens when that pollen grain travels on the wind or on the back of an animal and the body of an animal to another flower is that it lands on the female reproductive parts. So if you're looking at something like a lily in a vase, that's the big green chunky bit in the middle. and then the pollen grain grows through that female reproductive structure and releases the sperm cells next to the egg cells so they can fertilise them, produce the seed and the next generation.

You make it sign very simple. It sounds if it took millions of years to perfect it. It did indeed take millions of years to perfect, which is why actually there are still some plants that don't do it. So plants that have been around a long time had alternate ways of doing sexual reproduction. This pollination is unique to the seed plants, which are most of the plants around us and the most successful ones.

But I threw away millions of years. You do mean millions of years. I do mean millions of years. About 300 million years. Yes. What about the pollination of trees? Yes, the pollination of trees is much like pollination of anything else. A lot of our British trees are wind pollinated.

So things like oaks and beaches, birches, willows. And actually that's why you get hay fever, because those big trees are throwing all of this pollen out into the air, hoping it will get carried around to another tree. A lot of it ends up in your nose and you end up sneezing. But of course we have animal pollinated trees too. If you look at an orchard in spring, then a lot of those trees. With the flowers that look like your conventional flower,

an apple tree flower has five pink petals and it looks like a flower, those are pollinated by insects. Bees are really important in apple orchards. Why do plants tend to cross-pollinate? So unlike most animals, most plants can produce both male sex cells and female sex cells. And so if you can do that, and some animals can too, things like snails, then you can in principle self-fertilise. So you could fertilise your own egg with your own sperm.

But actually that's not really in the interest of the organism because it results in much less variation and the offspring tend to be less fit, less healthy. And so it's better to cross-pollinate, to take your pollen grain from individual one and fertilise the egg of individual two with it. But of course, as we've said, because plants can't move, they can't do that themselves.

They've got to use somebody else, an animal, usually, sometimes the wind or water, to carry that pollen for them. And that gives them the cross-pollination, which gives them more fit offspring. How do they know cross-pollination works better than the other way? So most plants have the ability to do both. I keep saying most because in all biology there are always exceptions to everything. But most plants have the ability to be cross-pollinated or self-pollinated. There are some that specialize on self-pollination, and there are some that are like animals that are actually only male or only female.

but the vast majority can be self-allocross-pollinated. And what will tend to happen is that early on in their flowering season, they'll be relying on cross-pollination. And then if they haven't actually produced any offspring, if they haven't received any cross-pollant, then they may actually self-pollinate later in the flowering season so that they still reproduce. So it's a sort of belt-and-brace's approach.

Thank you. Lars Chitka, how does insect pollination fit in with other pollination methods with wind and water and birds and other animals? Well, in comparison with... wind pollination. Of course, animal pollination is much more directed. So if you imagine yourself from the vantage point of a male plant, let's say, producing pollen, plant sperm, and you have to get the sperm to female plants, then of course using wind is an incredibly inefficient manner of doing that. You're throwing lots of sperm into the air, basically hoping that it'll

somehow get to members of the same species, female members. And so it's tremendously wasteful. A lot of it will reach the wrong plants. A lot of it will just not reach any recipient plants at all. And a tiny fraction gets to female conspecifics. So in comparison to that, employing pollinators like insects, for example, is of course a really clever way of getting the pollen in a directed way from one flower to another.

And of course, in doing that, you number one, you save a lot of wasted that otherwise would not land on its target. The other is that you have to do something about it. You don't have to do anything to employ the wind. But with pollinating animals, you have to give them something. You have to provide them with nutrition. And one nutrition is the pollen itself. So many insects eat pollen.

as a protein source plus nectar, which isn't there by default. You have to invest into feeding these pollinating animals to ensure that they're coming back for more. How do they do that? Is the nectar waiting inside the plant? Exactly. So it's generated by glands, nectaries inside the flowers. And this is where, of course, the pollinators also land to pick up the pollen. But the other thing that you have to do, if you're stationary and you can't move over to your sex partner,

is you have to build a signal to be visible and memorable to the pollinators. So you have to build flowers, which are not a necessity in wind pollinated plants. When we think about pollination, we may have honeybees in mind, but bumblebees and hoverflies and wasps and moths and butterflies and beetles also pollinate, Which insect are important for pollination and why? They're all important. So you're right. Many people just think about the familiar honey bee

because that's a domesticated animal that also generates honey for us. But it's one of about 20 to 30,000 species of bees that are out there. There's a tremendous diversity. In what way? Sorry. How are they diverse, these little things? How can they have 20,000? 30,000 diverse forms?

That's a good question. So many of these species, but just a few hundred of them, are social. And that, of course, is the most familiar way of bee life to have a colony with a queen inside it. But that's by far not all the bees. There are lots that are solitary. They are all single mothers where one individual builds a nest and provisions the offspring. And they differ tremendously in their nesting.

habits. Some nests in abundant snail houses, others in holes in wood or in cavities in stones. And especially in the case of bees, their lifestyle includes generating, collecting, a surplus of food that is not just for themselves, but also for their offspring. So they're very active in moving between flowers for their own good to harvest as much of a surplus in nectar and pollen to ensure that they can raise lots of offspring from it. And you've also, of course, mentioned other pollinators, such as butterflies, beetles that don't build nests at all, but they still use the same resources provided by the flowers that is protein via the pollen and nectar as a carbohydrate drink. Jane, can you give us more detail about pollen and about nectar?

Yes, nectar is a simple solution of sugars. Pollin is a really complex brew of proteins and lipids and minerals and vitamins and all sorts of things. We think of it as this yellow dust. Okay, it's the stuff that makes you sneeze. It gives you hay fever. First of all, it's not always yellow. Something like Vipers' Beelgross has blue pollen, which is very cool. And secondly, if you look at the dust under scanning electron microscope, they're like

alien spaceships. Different families of plants have got very different looking pollen grains. So they can be round like the moon with holes all over them, like craters. They can be covered in spikes. They can be lozen shaped. And they're ridiculously diverse, and we don't really understand. They've got very fine scale sculpturing over the outside. They're incredibly beautiful.

So even, you know, you bog standard, a daisy pollen grain is a very beautiful thing. So these are the kind of two commodities that are on offer as payment, effectively, for that taxi service of getting your pollen from plant A to plant B. Do you want to come in there, last? Yes. So I think an added degree of complication in that interaction is, of course, that bees have to be careful shoppers in the flower supermarket. That is, they have to compare what's on offer from different plant species

in comparison to the cost of getting to the flower, of the effort to manipulate the flowers and find the way to the nectar, and memorize those flower signals that offer the best cost-to-benefit ratio. So in the flight range of anyone bee nest or hive, there might be several dozen different plant species all differing in the value of these rewards. And you have to remember the signals. The yellow ones that are bilaterally symmetric

might be just the ones that are offering the best rewards. You remember them, you disregard other flower species, and just as an individual, focus on those plant species that you have experienced as the most rewarding. So you have to be a good shopper. You have to make comparisons of prices and benefits in the same way as human shoppers in a supermarket, where let's say you memorize your favorite toothpaste by the packaging.

You've found the price is reasonable, the quality is good, let's remember that package and return to it the next time. And that, of course, is what plants ideally want to be memorable so that your customer stays with you, not your competition from other plants. Jane. I was going to say, the backdrop for everything as well is plants don't just sit there looking pretty. They manipulate and train pollinators to go where they want to. So if you think of something like a foxglove,

they'll be out in flower in May, a tall plant with bell-like flowers all the way up the top. At the bottom, the plants put more nectar. So if you watch a fox club in summer, as you sat there with a cup of tea or glass of wine or something, the bees will always start at the bottom. Okay, so they're bringing in pollen for another plant. They're loaded with pollen.

They then pollinate the plants at the bottom. They'll work the way up the spire. and as they leave the plant, they'll take the pollen from the foxglove to the next plant. So those foxgloves are training bumblebees to kind of give the best service. Everly, just been mentioned anyway that plants pollinating themselves, what circumstances were bringing them to do that? So self-pollination is always an option for most plants, and I think of it as a sort of reproductive fallback.

It's not ideal. It's much better to do cross-pollination, because if you think about a red lily flower, cross-pollinating a white lily flower, You might get red flowers in the offspring. You might get white ones. You might get pink ones. You get variation. And that colour doesn't necessarily matter,

but that applies to all the genes and all the traits of the plant. And that variation that you get from cross-pollination is really important for evolution, because it's the material that evolution works on. It needs a variable population to work. And we think of cross-pollination and cross-fertilization is so crucial because if you don't do it and everybody else around you does, your competitors or your herbivores or your peopause,

or your pests and diseases, then they're going to evolve faster than you, and that's bad. You're going to end up in trouble. So that's called the Red Queen hypothesis, after the Red Queen in Alice in Wonderland, who said you had to run fast to stand still. Now, self-pollination doesn't give you that advantage,

but it's better than not reproducing at all. So if you're a plant that's growing in an environment on your own, then, hey, you could self-pollinate and you can produce the next generation. What examples are there of that? So, I mean, if you're the only bird landing on an island, you're going to die out. if you're the only plant planting on an island, you can self-pollinate. Actually, most familiarly to listeners, is the weeds in your garden.

So weeds are evolved to occupy habitats that are disturbed, so ground that's been recently dug over. They arrive, they might be the only one there. That's fine. They can self-pollinate, set seed, and then next year you've got an awful lot of weeds in your vegetable patch. And this is widespread, or are you talking about occasional? Actually, you can see it if you look at a flower,

whether it's adapted to regular self-pollination or not, because if you look closely at the flowers in your garden, if the male reproductive structures are those anthers with the pollen dust on them are sitting close to or at the same height as, or even above the chunky green female reproductive structure, then the pollen's likely to fall onto it and you'll get self-pollination. Whereas actually, if you look at most flowers, you'll find that the anthers are sitting far away from

or below the height of the green stigma so that they can't self-pollinate. It is fascinating in the complexity that seems you describe with such fluency. Can we just go back to something we just touched on Lars. How far back in evolutionary history does pollination go? And how did people discover the process? Yeah. So, of course, we don't have fossils of behaviour. All that we do have is the odd insect that might be embedded in ember

and that has the mouthparts or structures to collect. Why would be embedded in amber? Sorry to interrupt you. Why would it be embedded in amber? because it landed on a tree that had a bit of resin when it was still in its liquid form and unfortunately got trapped there and then presumably drowned in more resin. And occasionally we are fortunate enough to find bees or other pollinating insects in that sort of setting. Otherwise they wouldn't fossilize very well because they don't have bones.

But of course from these finds we can deduce how ancient pollinating. is. But of course, our more recent finding about the complexities of behavior, they can only done with bees that live nowadays whose behavior we can observe in the laboratory and in the wild. And in doing that, we have found, for example, that quite a bit of the harvesting of nectar and pollen at flowers needs to be learned. Bees are not pre-programmed to extract these commodities. often natural flowers like snap dragons for example are like puzzle boxes where bees have to figure out how to open them

how to pry the petals apart and how to manipulate the structure to extract the rewards and a naive bee that's never seen a flower before is spectacularly clumsy at that so it often takes the minutes to open a flower for the first time but they do learn it over a few dozen visits

and get increasingly efficient and manipulating these structures. And that, of course, is something that we can't capture from the fossil record. This business, you talk about visits. They seem to be able to go up to 10 kilometres looking for the same flower. Have you any accounting for that? It's extraordinary on barren territory to most people. Indeed.

Over there, 10 kilometers away is the flower I want to go and work with. Indeed. So a few years ago, we marked a few thousand bees. in East London, Queen Mary, where I'm based, with little number tags, and we invited the public to look in their gardens, say, can you find our bees? And the furthest records were in Hyde Park, which I think was about eight kilometres from these bees' home base, and the bees would shuttle back and forth regularly between East London and Hyde Park.

Would they go to the same places every time? They remember the particular patches where they have found rewarding flowers and return to them every time. And that, of course, involves memorizing the entire landscape, cityscape along the way and reliably finding your way back. Because if you don't, you're dead. There's a very strong selection pressure to memorize the point of origin, the location of your home.

It presumes in this tiny insect, an enormous amount of intelligence. So their brains are indeed tiny, about a cubic millimeter or something. size of a pinhead. But that doesn't mean their brains are simple. So everything in a bee's brain is very elegantly miniaturized in the same way as I guess computing equipment is elegantly miniaturized in a mobile phone. And their brains are immensely complex little biocomputers that can store long-distance routes. As we've just discussed, they can store the signals that the flowers put on display and the motor patterns that are required to open the flowers. Do you want to write to that?

Yes, just to say that we know that insects have been pollinating plants for a long time because we can find fossils. Fossils going back 250 million years of insects, beetles, but also some flies recently, with fossilised pollen attached to their mouthparts. So they're clearly feeding on flowers or flower-like structures. They're picking up the pollen and they'll be moving it between different plants. I mean, Leris has done amazing work understanding what bees do and how they make decisions.

and some of the things that have come out of our joint work have been astonishing to me. So not just that the bees are choosing like the toothpaste you suggested based on what they like best or what has the best reward for them, but they're calculating within those decisions how much energy they're spending in actually manipulating the flower. So if they have to open a complicated flower like a snap dragon, if the flower's slippery and they have to struggle to get a grip on it, those calculations, the energy they spend go into the calculation of the energy they get out,

and help them make those decisions. And that to me, I think, is the most astonishing thing. And that those calculations are based not just on the energy for the individual B, but also on the maximum rate of return of energy back to the colony and to the larvae. So really complex decisions being taken about the whole community. Do you want to add to that last? Indeed, and the number of flower features that are learned and play a role in these decisions is astonishing. So it's not just the rewards, next.

and pollen and the color and scent signals that advertise these. But bees also remember things like iridescence. Some flowers are very shiny and change their color appearance depending on the vantage point from which you look at them. And that too is learned by pollinators. They can even learn to use electric fields surrounding the flowers in which tell bees how recently a particular flower has been visited. And if that's the case, if it's been just visited by a competitor, then there's no point of going there again because it's going to be empty. And bees can use these electric fields to judge how recently a flower has been visited. Chairman, you'll have to come in here. Yes, I'll come in them. So bees are truly

wonderful little insects. They're very good at being a bee. They pollinate flowers. They raise broods of young. You have to put them in the context of a much bigger community, though. So bees are, we work at the whole community of pollinators and whole communities of plants at any one size. Every flower in our system and every pollinator gets kind of counted in and counted out. And there's a huge range of other things. So bees are kind of the pinnacle, I guess. They're certainly in terms of, I guess, IQ or something. They're the smartest. They can learn things. But there's a huge range of flies out there of beetles, of butterflies, of moths is the night shift that comes out, which is really hard to study because you have to bumble around at night.

So, but the flies, flies are incredibly diverse. And what you need, what a flower community needs is a diverse. of pollinators visiting it. Because actually, you know, as climate change, the biodiversity crisis and all the kind of things that are happening in the background go on, you want lots of spare parts in your system. You know, there's about 24 species of British bumblebee. All bar six are declining. So the more other things that can do the job as well, they give you that kind of redundancy,

that kind of ability to still get your pollination done. So flies individually generally aren't as good. There are some specialist pollinating flies, probably one of my absolute favorite insects are the bee flies. These are a little bomboliddy. If you imagine like a flying teddy bear with a hummingbird-like nose and it can fly upwards, backwards, sideways

like a Harrier jump jet. And they hover in front of primroses and pulmonary at this time of year. And actually Bristol-R-M-based is the only place in the world. They're kind of common for about a month in your garden. You'll find them on the primroses and primulars. But those are specialist pollinators.

And equally bizarrely, as larvae, they actually parasitized solitary bees as well. So their larvae are eating other bees And as adults, they're pollinators of plants But there's a huge range of other flies out there You've got your hoverflies They're just tachinids So there's lots and lots of diversity to be found on flowers

Come in And although we talk about flowers And the things they do to attract bees They also have specialist adaptations To attract this great diversity of pollinators That Jane talks about as well So I actually brought a photo to show you, Melvin This is actually a bee fly

The sort of... This is perfect for radio that Jane was just talking about I know the listeners can't see it, but as Jane described it, it's like a little flying furry teddy bear. The amazing thing in my photo is that it's sitting next to a spot on the petal of a daisy. So here's the daisy, and you can see it's got three of these big black spots on it. And if you look closely at the spot, it's shiny. It's got these little white patches that mimic the white patches of shine on the fly itself.

And actually this daisy, it's the South African species, is mimicking females of this beefly. And so these spots look to the male fly, like a female fly. It comes in thinking it's going to find a mate. It bumbles around in the daisy going, well, where did she go? I'm sure there was a girl here. And in doing so, it gets dusted in pollen and does the great pollinator job for the flower. So although we tend to focus on bees, James Wright, the diversity of pollinators is astonishing.

And the diversity of tricks that flowers use to interact with them is also amazing too. I mean, there are 350,000 species of flowers out there. That's 350,000 different ways of signaling or advertising. Jane talked about the patterns on the foxglob, so the little row of spots coming up the centre of the foxglove flower is actually a little guide, a little landing lights to the bee. So you can start to look at flowers in your own garden in different ways. But once you start looking at that enormous diversity,

you see amazing things, something like Jack in the Pulpit, Lords and Ladies. These are actually attracting animals that are trying to lay their eggs on what they think is rotting flesh. So they produce scents and smells and colours that look like bits of dead meat and along come insects that lay eggs that will hatch into larvae.

While they're there laying their eggs, they get dusted in pollen. So the pollination happens. But of course, when the larva hatch, there's no meat for them to eat and they die. So these are the flowers tricking the plants. And some of the flowers that do this, I mean, there are astonishing examples.

My favour is the Titan Aram. So it's a native of Sumatra, so not something you'll see in your garden. But it not only does this colour and scent thing, it also heats itself up to 37 degrees centigrade to mammalian body temperature in order to improve that mimicry and make sure that it really does a good job

of looking like a recently dead animal. Now, as you want to come in here? The diversity is becoming more and more amazing as this conversation goes on, the mind of intelligence involved and the variety of intelligence involved. Indeed. So on the side of the plant, of course, there is no intelligence.

So what we're seeing here, these flowers mimicking female bees, of course, haven't got there by intelligent processes, by any kind of innovation, but by evolutionary trial and error processes. But of course, on the side of the pollinators, there is a tremendous amount of intelligence going on that goes into making economic decisions. And it turns out that in bees this has gone so far that they're even smart at some tasks that evolution hasn't directly prepared them for. So bees can count, they can recognize images of human faces. They can even manipulate tools in a simple manner and learn such techniques by observation. So there are challenges there that presumably in their origin date back to the need to be intelligent in their harvesting of food,

but their problem-solving capacities go way beyond what nature generally puts in front of them. Although I always think that it's the diversity of flower forms that's most exciting, I should admit that the insects get away with quite a lot of cheating and tricks in this system too. And one of the classic ones

that people might enjoy looking for in their own garden is what we call nectar robbing. So from the plant's point of view, if you think about something like a foxglove or a snap dragon, what the plant would like is the insect to go in the front, access the nectar and get dusted in pollen. But actually, if you look at those flowers in your garden,

you'll often see little holes drilled in the back of them, and you'll see bees coming and landing on the back of the flower, sticking their tongue in and sucking the nectar out and not actually going anywhere near the pollen or the reproductive organs. So no pollination happens, and the reward is stolen. So we call that nectar robbing. And it's something Lars would be interested in this. It's something that we see as a learned behaviour.

So early in the season, not that many bees know how to do it. as you go through the season in your garden, more and more bees figure it out, probably from watching each other, but also from finding the holes. And so actually pollination's success, as far as the plants are concerned, decreases over the summer. You're more likely to get pollinated early on when the bees don't know how to do this than you are later on. Jane. Yeah, well, picking up on the topic of food, of course, pollinators are incredibly important

in food production for humans. So that pollination leads to the pumpkins and raspberries and apples and so on. And why just that and why the pumpkins and apples and so on? Because they're insect pollinated plants. There's a whole range of plants that need most, I think it's something like 70% of crop species need animal pollination. And if you think about human diet, most of the calories in our diet, so things like the wheat and the maize and the rice and so on, those come from wind pollinated things. The micronutrients, so the vitamins, things like vitamin A and folic acid and various other things come from insect pollinated crops. And so in places like London, that doesn't really affect our diets usually because we just go to the supermarket and you can buy anything pretty much at any time of the year.

But if say you're a smallholder farmer and 84% of the farmers in the world are smallholder farmers, so they eat what they grow on their farms and they sell a small amount, perhaps of a cash crop, those pollinators are really important because if they don't get enough of those insect pollinated crops, they don't get the nutrients they need. So we're working in a series of villages in Nepal. and in our villages, 50% of the kids are stunted, and they're not stunted through lack of calories. They're stunted through lack of those micronutrients in their diets, because those allow you to kind of grow and grow healthily, reach your full potential. Green leafy vegetables are really important.

And so what happens is if you look at the minerals in the diet of smallholder farmers, you get these huge peaks, so there's a time of year when they're eating mustard leaves. Now, mustard aren't the result of a pollinator event, but if you want to grow mustard the following year, you need your mustard, pollinate it to get the seed to grow again. So you don't just pop down to the garden centre to buy your seeds. You actually need them, you know, as well as eating the crops, you need the seed collection for next year's crops.

So for food production, pollinators are really, really important around the world. Jane, in your Nepal setting, is protein important from plants as well? Because I have a similar project in Kenya, and it's actually the pollination of legume crops, of beans and peas that's really important for the protein in the diet. It is. These people eat very little animal protein. So beans in the crop are where most of their protein comes from. So it's protein, it's vitamins, it's minerals,

it's a whole range of things. What's the positive, well, the negative side of that is as pollinators are declining, and there's about a 10% year-on-year decline in the elderly bees. It's used to pesticides, it's used to climate change, it's used to habitat loss. The normal things that are happening the world over are leading to pollinator declines. The smallholder farmer can't afford to kind of use kind of a high-tech approach to solve those sorts of things.

It can't put more fertilizers. He or she can't put more fertilizers or use insecticides. But what they can do is actually if they look after their pollinators, they can actually improve the seed set of their crops. So things are apple crops, which are the cash crop in our bit of Nepal where we're working. If you look after your pollinators by having the right flowering plants there throughout the year, by providing habitats for them to nest in, you can actually improve the value of your crop. What are the best and worst conditions for this then?

For insects, it depends whether you're urban or rural. So in urban habitats, so here in, I'm commuted from Bristol into London today, your suburbs tend to be really good. So gardens are fantastic. And in Britain, gardens make up about a quarter to a third of a city. It's remarkably consistent. About between 1 and 5% are allotments, allotments are truly fantastic. But if you go to rural areas, the good places there are any natural or semi-natural habitat.

So something like Calcareous Grassland, which is the grassland you get on limestone, fantastic for nectar production. Farms where farming is less intensive, so organic farms, some of the regenerative farming systems, where you've got more semi-natural habitat. What's really bad for pollinators in the countryside? is intensive farming. Whatever the type of farming, if you're doing it intensively, there tends not to be much space left over for wildlife

and pollinators are pretty thin on the ground there. The word decline has been mentioned once or twice, but it might be more important than I'm suggesting, is it? Well, it is indeed a major concern, of course. And if you ever have the privilege to fly, just looking at our landscape from above, it's just staggering how little nature there is left in any kind of arable surface to the extent that it's flat, not mountainous, it's used for agriculture.

And the tiny bits of hedgerow or riverside meadows are on the range of a percent or less of the surface in this country, for example. And of course all the green that you still do see, even if it has some flowers, of course, is thickly covered in pesticides. And therefore, to some extent, toxic to pollinators. and we can't afford to lose them because obviously we need them to pollinate the crops. We need them to pollinate our pretty wildflowers, but we also need them more generally for functioning ecosystems. The pollinators, to some extent, are canaries in a coal mine. There are, of course, lots of other insects also affected that in turn feed birds and so on.

So there is a bit of a disaster scenario out there in the countryside, perhaps counterintuitively urban spaces are now often a refuge for pollinating insects because there are less toxic substances sprayed and there's more of an effort to put flowers out there because they're pleasing to the human eye and good for pollinators. Jane, you're going to say something. I'm just going to say, I absolutely agree with everything last says. There are some positive.

There's some little glimmers of hope out there again because it can all get very depressing, actually, if you think about all the decline side of things. firstly pollinators breed quickly. So if you want to restore them, it's not like trying to restore albatrosses or elephants or something within a couple of years. If you get things right, they will come back quite quickly. And there are some, Britain's actually doing some really quite world-leading work in kind of conservation at the moment. So the new agro-environmental schemes are coming in, environmental land management. It's a really ambitious way of dealing with some of the

problems of biodiversity declines in the countryside and doing carbon and doing flooding protection as well. to me, you know, the sound of summer in the garden is when you're sat there in a chair on a warm summer evening listening to the bees buzzing in the borders and watching the butterflies on your buddlier and so on. And so there's a lot you get back from those sorts of schemes. So you're an optimist? Are you an optimist? I think botanists are always optimists because we're so used to looking at this enormous diversity of plants that on the face of it should be eaten, can't move, don't have intelligence, as Lars says, can't make decisions. And yet actually they survive, they flourish.

evolution comes up with ways for them to work. And I'm sort of optimistic that life will continue to manage that. I am perhaps less of an optimist than my colleagues. I think that the planet, of course, in general, is at a very crucial period when we may be, if we really put the feet on the brakes hard right now, can still change things around, but it might be getting close to a point where it's too late. Too late for what? To my knowledge, a very important. A very important. A very much. A very large percentage of bee species are already under threat. There are none of them extinct yet in this country or globally. So there might still be a chance. But of course, to reestablish them, we need a lot more wildflowers for these bees to feed on, a lot more wilderness for them to

find nesting possibilities. The nice thing with bees, of course, is that everyone can contribute a little bit to the extent that you have control over what you plant in your back garden, or even on a balcony in a high-rise building, you can actually contribute by providing the kinds of resources that bees need, that is flower resources, or leaving a bit more of a mess in your garden for them to find nesting locations. Beverly, some insects pollinate only one type of plant, others are generalists and why? Yeah, so it's not the case that they only pollinate one type of plant. It's about how many different types of plants they're feeding from.

And you have to think of it, or I always think of it from the plant's point of view too, which is how many types of animals are coming to pollinate it or actually doing the pollen transfer for it. And if you think about something like a daisy, it's a big open flower, almost any animal can land on it, they can find the nectar and the pollen. There's no need for any kind of specialisation. But the classic example of specialisation is an orchid from Madagascar. called Angrekum, Sesquidali, which has a nectar spur,

so that's a tube that comes off the petal, and the nectar sits in the bottom of it, and that spur is 30 centimetres long. So there's no way your average beetle or bee or fly can get to that nectar. And when Darwin was shown this orchid at Q, he said, well, there's going to be a moth with a tongue 30 centimetres long that pollinates that,

and everybody laughed at him. And it was actually after he died, that the moth was found. And it really does have a 30 centimetre long tongue. It flies around with it rolled up, in a ball hanging beneath its body. And when it finds one of these flowers, it's able to actually dip its tongue into the nectar spur and get the nectar.

So a flower like that has gone down the route of what we think of as specialisation. It's not wasting resource on any beetle or fly or bee that comes along. It's got a very specialist relationship. And when the right moth comes along, a nectar is drunk, pollen lands on the moth's head, and then it's transferred to the next flower. But it's a very different strategy to the daisy strategy. Lots of the daisies pollen will end up on all sorts of other flowers

because bees and beetles and flies go everywhere but it's less risky in a way it's not putting all your eggs in one basket so some plants go for the specialisation some go for the generalisation We've been talking about intelligence a lot of the time here last Should we regard pollinators as intelligent in their decision making Would we use that word?

By all means So I think that the learning that goes into remembering which flowers are particularly rewarding how to manipulate them, how to find the way to them is by all means intelligent behavior. It's not hardwired. They're hardwired in the same way as humans are hardwired to learn language, but bees have to learn the way to the flowers, how to get the nectar and the pollen out and so on. Now that doesn't apply to all pollinators. There are, of course, in the same way as there are specialist plants that rely on certain pollinators to deliver their pollen. There are also bee species, pollinator species that

are relatively specialized, whose evolutionary ancestors were generalists, were visitors of many species, but who over many generations have become specialized on just a narrow limited number, sometimes one flower species to get their resources from. And of course, these are most at risk from climate change. So if the flower species should become extinct, the pollinator goes with it. If the flower species, because of climate change, moves its phenology, the time of flowering just by a few weeks out of sync with the pollinator, again, the pollinator is dead.

So specialization is often a way. one-way street when any kind of environmental evolutionary change happens and climate change might lead to just that sort of desynchronisation that's very dangerous for specialist pollinators and their plants as well. May lead. Is there any chance that you think it would lead to extinction? Certainly in some countries. So in Hawaii you've got a bunch of tree lobelias and specialist pollinators that feed on those,

the specialist pollinating birds, those birds caught aviomero. malaria, which was bought in by other birds that were introduced, the pollinators are lost. And yeah, some of those plants now are reliant on almost hand pollinator. You know, that's the only way they're going to get pollinated. So certainly around the world, there are examples where pollinators have gone extinct. The specialists are very much a minority there. Most plants are visited by lots of different pollinator species, and most pollinators visit quite a lot of plant species as well.

So the norm is this kind of generalised system, which is actually a safer system than the specialisation. but it's a trade-off. You know, it's like having a bespoke servant that does your pollination for you, and that's all they do versus lots of people that all may or may not kind of help. So it's a different approach. Lord, you come in.

Yes, just to say that actually on the sort of positive side that life finds a way around these problems, I mean, in some of those examples where the specialist pollinator has gone extinct, we find other things stepping in and doing the pollination. So one of the stories I like from Hawaii is the rats that have taken over pollination of some of the systems because they're smart enough to work out,

there's food in the flowers and as far as the plant's concerned, anybody that moves the pollen around will do and if it's a rat, it's fine. Well, I think that's a sufficiently elegant ending. Sorry to end up. Thank you very much. Jane Mehmet, Lars Chitka and Beverly Glover. Next week, the Persian king Cyrus the Great, who founded the largest empire of the world had ever seen, but whose reputation for greatness has since been questioned. Thank you for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests. Starting with you, Lars, what would you like to have said you didn't get time to say?

Well, so beyond our and other studies of B's remarkable intelligence, we've also discovered in recent years that they're most likely sentient, that they have the capacity to feel emotions, including being an optimistic or pessimistic states. How do you find that out? Various tests. So one version of a test for emotion-like states is basically using the proverbial glass

that's either half full or half-empty, where you have a physically ambiguous stimulus, a glass that's just filled with liquid to the middle. And an optimist judges that situation is, oh, that's still pretty good. There's still a lot in there, whereas a pessimist looks at exactly the same stimulus and says, oh, my God, it's almost all gone, and is all sad about it. And we're using, we're taking that sort of setting into a laboratory by first training bees,

for example, that a certain color is always good. Another different color is always non-rewarding. And then we're facing it with a color that's halfway in between, the ambiguous stimulus, the glass that's 50% filled. We're then asking, how do you judge this? Is this more likely something good or something bad? And it turns out that if something good happened to the beast before they even start the experiment,

if, for example, they've received a little surprise reward before they're starting the test, that ambiguous stimulus is judged much more optimistically than it otherwise would. They get a little dopamine hit. Dopamine is the transmitter involved. with such optimism as it is in us, actually, it's the same in bees, and they then judge this glass 50% filled as more likely being something good.

If on the other hand, what happened to the bees before the experiment is a simulated predator attack, where they just so got away, they're judging that ambiguous stimulus as more likely something negative. We've also discovered play-like behavior in bumblebees, where they actually seem to enjoy the activity of rolling a ball around. and most likely they also experience pain-like states. So there is a range of emotional states in these bees. And that to me, I guess, lends another perspective on the need for their conservation.

The arguments we've heard earlier, I guess, are related to bees' utility. They do something important for us that is pollinator crops and they generate color in the otherwise green world, terrestrial world, by pollinating flowers in our gardens and in nature and so on. But that's an argument from utility. They do something useful for us, so let's conserve them. But to me, once you recognize that an animal is likely sentient, there is also, I guess, an onus, an obligation to,

with regards to their welfare, the obligation to look well after them to ensure that they don't suffer. And you? Matt, let's bring in the kind of conservation of pollinators, is reversing those declines. So one of the things we've learned recently is that just the way that different flowers have phonologies, you know, your daffodils are out now,

whereas other things are flower in the summer and ivy flowers in the autumn, whole habitats actually have a phonology. So if you're looking at conserving pollinators at the landscape level, having a number of different habitats around is really important. So if you imagine springtime in a woodland, you've got your bluebells and your red campions

and all sorts of things that flower in early spring. And then there's pretty much not much else the rest of the year. If that happens to be next to a meadow, though, that meadow will be flowering in May and June. You'll get all the hay meadow plants coming out if it's an ancient meadow. And then again, if that's next to a heathland, you've then got the summer heathers and Erika. So having that patchwork of habitats in a landscape is really, A, it's really important for pollinator abundance and diversity and lots of other species. But there's also some evidence that actually if you've got a mixture of habitats, it gives you some protection against species loss as well. So it's that landscape level conservation is the way that we need to be thinking about things.

And one of the reasons that gardens work so well is that people, they don't have so much of a phonology because we like flowers all year round. So as gardeners, we're constantly making sure we've got, you know, flowers pretty much from now. I've got the first pulmonarys out in the garden right now. And I want flowers in my garden right through till kind of, you know, November, December, when the lust of the bumblebees will disappear. So gardens are really good. And it's that empowerment to the individual. There's not much that you personally can do about conserving. well, albatrosses and elephants and things,

but there's a lot you can do for the solitary bees in your back garden or on your balcony or any little bit of space. Or if you haven't got a garden, and it's a reasonable proportion of people that don't have their own gardens, join a friends of a park group. There's all sorts of ways of getting involved in conservation. And, you know, it's everyone working together, I think, that will make that difference. Are you worried, Jane, that this is on the way out?

What's on the way out if it's on the way out? Yeah, I guess I'm a cup half full sort of people. person, I guess, but it's hard some days. And actually, just speaking of one lastest's comment, I have a very untidy back garden. There is a lot you can do as an individual to help. We need to look at some much bigger questions. So farming is one of the reasons that things are declining in the UK and worldwide, how we actually produce our food. If you look at Britain, I think it's about 70% of the land area is farmland.

And most of that is for rearing livestock. Lifestock actually puts rather few calories into the food chamber. It's a big part of our kind of cultural life, Sunday roast and all that sort of thing. It's not about everyone becoming vegetarian, but people eat less meat. And we actually, if we gave up some of, you know, the land that's just used for livestock, and that was used for biodiversity, for carbon, for flood protection, that would lead to, you know, not many calories leaving our food chain, but would give a huge amount of space for doing other things with that land.

Because it's not just the land that you're, it's not just the grass that the livestock needs. We've grown an awful lot of wheat for feeding livestock. So a huge amount of our British farming system is orientated around livestock. Beverly Glover. I think one of the difficult. Particularly with intensive farming as well, is just the sort of the idea that there's loads and loads of food available in a very short window, depending what the crop is. But if you think about fields full of oil seed rape, you know, from the bees point of view, that looks great for about two weeks. And then all of that land is empty of flowers for the rest of the year.

And you've got a colony to maintain for the whole of the season, at least, or the year, depending what sort of bee you are. So intensification by focusing on individual single monoculture type crops creates this, this, this, of boom and bust problem for pollinators. And that's why diversification of farming and having wildflower margins, having gardens around about, makes a big difference because it gives you food throughout the whole season. And that's the really crucial thing. We've measured the decline in pollen at the scale of the whole of the British Isles since the industrialisation of agriculture.

And since then we've lost about a third of the standing crop of nectar in Great Britain due to intensification of farming. So you can measure nectar. It's really straightforward stuff to work on from many points of view. pollen is way more complicated and we're only just starting to get to groups with what's in it and there's real differences between different families of plants

and I think over the next kind of three, four years, two, three years, we'll know a lot more about pollen because the chemical biologists are starting to analyse what's in there. And different types of bee probably need different building blocks to rear their larvae. Well, thank you all very much indeed. That was fascinating. Marvin, would you like tea or coffee?

I think I have another cup of tea, please. Tea? Coffee please. Coffee? Tea, please. Tea, and Lars had to go to another appointment. He did. Two teas and one's coffee.

In our time with Melvin Bragg was produced by Elian Glazer and it is a BBC Studios audio production for Radio 4. I'm Helena Bonham Carter and for BBC Radio 4, I'm back with a brand new series of history's secret heroes. And he tells her that she will be sent to France as a secret agent. She will work undercover. and if she's got, she's going to be shot. Join me for more stories of unsung heroes,

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