Instant Genius - Flies, with Dr Erica McAlister

Episode Date: October 20, 2022

Yes, we moan about them biting us, landing on our food and invading our picnics, but did you know that flies are extremely important pollinators? And they also polish off a lot of the dead and decomposing stuff in nature, making the world a better place for us to live? Dr Erica McAlister, the curator of flies at the Natural History Museum, tells us why we should give these insects a little more love. Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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I'm Alice Lipscomb Southwell, the managing editor at BBC Science Focus magazine. In this episode, I talk to Dr. Erica McAllister. Erica is senior curator of flies at the Natural History Museum and an honorary fellow at the Royal Entomological Society. She's also the author of the books, The Secret Life of Flies and The Inside Out of Flies, which are both available now.

In this episode, she tells us all about flies and why we should learn to appreciate them just a little more. Hi, my name's Dr. Eric McAllister, and I'm a senior curator of flies and fleas at the Natural History Museum in London. Now, flies are a super diverse group of insects. So what exactly is a fly and how is it defined scientifically? Oh, so I'm going to tell you what a fly is, and I'm going to tell you every time that a fly lies to you,

because they've taken what is the blueprint of their design, and they've run with it. So they're incredibly morphologically diverse. So when we first say what is a fly, a true fly, they're in the order Dytra, Diterra, which is two wings. So straight off, that is one of the diagnostic features of a fly. The adults have one pair of wings, these two wings. And whereas most of the other insects will have two pairs. So beetles have two pairs, bees, whilst,

and ants, two pairs of wings when they have them, etc. This second pair in flies has been modified into what we call a halter. And this halter is this balancing organ. It basically enables them to be the best aeronautical engineers out. They, you know, they can land upside down, they can fly around the planet. They are amazing because there's balance in organ. And the third thing is sceptorial mouthparts as an adult. So you actually can't be bitten by a fly. So you can be sliced and maimed and pierced, but you can't be bitten. So they have this sucked where your mouth parts. But this is obviously we're just talking about the adult stage here.

But there's a lot of flies that don't have wings. There's a lot of flies that don't have any basic mouthpiles. And there's a lot of flies that don't have wings or hautez. So you're like, oh, thanks, fly. So all those things I told you, there's always an exception to the rule. So you've got all this diversity in flies, but how many species are there? described, there's about 165,000. But we're in the group called Dark Taxer, which is just the best title, isn't it? And so us and Hymanautra, the bees, boss and ants, we are probably massively underdescribed in comparison to our true diversity.

So the Beatles are about 350,000 described species, but we know that the flies and the hymenoptera are probably going to be more than that when we get round to it. we've just got some quite tricky stuff to deal with. Loads of small, tiny black flies. Well, I was going to say that any flies still waiting to be discovered, but I guess if you've not got your way through all the ones you already found, to describe them. Yeah, no, there was a shocking paper that came out, and we think it is a bit of a like, ooh,

that described one family a fly, based on morpho and molecular analysis and predictions, that one family had 1.8 million species in it. Yes. So at that point we went, oh no. So we know there's quite a bit to go, yes. Okay, well, getting down to maybe the simpler questions, what is the biggest species of fly out there? So the biggest species of fly is called it's Goromydas. So it's a type of panathalmid, which we don't get in the UK. They're called timber flies. and these can be like seven or eight centimetres long. Yeah, I mean, I was looking at a bat yesterday in the collection

and it was a bumblebee bat. So it's smaller. This bat was smaller than my fly. So I was like, wow, that's not bad. That's a chunky fly, isn't it? I mean, they look like what you would think of a horse fly. So they look like they're huge and scary, but the adults don't even feed. and the larvae take like five years to develop.

So they just look really hardcore and they're just wimps. So just get all their nutrition while they're in the larval form and so don't you to feed at all as adults? Yeah, and this is what most of it is. It's alternation of generations. The larval stage is the feeding stage. So this is really important when it comes to nutrient recycling and all these wonderful ecosystem of services that a lot of flies do.

So, I mean, it's an ideal life cycle because you spend most of the energy. of it just eating. It's brilliant. And then you have the adult stage for reproduction and dispersal. Great. And so at the other end of the spectrum, then, what's the smallest fly species? So it's in the group of flies called forids. This is a family of Faraday. And these flies do absolutely everything. But there's a guy, Brian Brown in America, who's just fabulous at describing these. And there's one that's been described at 0.4 millimeters. Oh, it's really tiny. No, it's tiny.

There's one that's not the tiniest, but it's very, very small that's been described amusingly after Arnold Schwarzenegger. So look up the Schwarzenegger fly. And it's minute, but it's got really chunky limbs. Oh. So they've named it after him, which I think's quite sweet. I mean, that's really tiny, isn't it? You think here in the UK we've got fruit flies, and they're pretty tiny.

But if that flies 0.4 millimeters, that's going to be, what, like half the size of a fruit fly? If you're talking toesophila, fruit flies are about three millimeters. They're massive. Come on, I mean, they're huge in comparison. So what is the commonest fly species in the UK? See, I don't know. Now, I was thinking about this.

Now, we've got about 7,000 species of fly in the UK, which is incredible. If you think there's more species of fly in the UK than their mammals described on the planet. Okay, just to put our fauna into perspective, And within those, you've got some very species-rich groups, and there would be things like crane flies and hoverflies and things like that. But when it comes to abundance, you probably are looking at something like the midges,

because you're going to get massive mating swarms coming up. And so those will be in thousands. But also every year we have like billions of hoverflies that landed our doorsteps each spring. And there's another fly, and Anthem Myard, that again, millions of them migrate across the UK. So, I mean, there's just millions and millions of flies out there. I think I did an estimate once that for every human being, there's 17 million flies. Oh, my gosh. But we need them.

That's a lot of flies. We do need them. We need them. Yes, I'm going to ask about that, because how important are there as pollinators? I think bees get all the spotlight, don't they? But are we forgetting about the flies? Of course we are. I know. Bees seem to have better press than flies. And I don't know where there is because of their big eyes and their cute faces. But when it comes to pollination, flies are incredibly important. Just mentioning those hoverflies, the fact that we have these four million turn up each year, four billion, I think it was, sorry, four billion that turn up each year. They are along the way, they're migrating across Europe. So they're doing pollen transfer as well. So it's really important for conservation, because they're, they're doing gene transfer. They're recycling nitrogen. So they're pushing nitrogen around. And then

they're coming here. And not only are the adults great pollinators, because unlike bees, they don't have to go home, you know, they don't have to give up their pollen. They just stuff themselves silly. Plus, they're very messy. So bees and bubble bees have lovely beautiful pollen sacks and they put them all in. So when they move around flowers, they aren't necessarily spreading them as much. Check out, honestly, check out the faces of hoverflies. They got pollen absolutely everywhere. And a lot of them will scrape it forward, and they have pollen combs on their arms, straightforward, to eat it.

But they don't have to go back home. So although they might not get as much pollen in each feeding event, just because of their activity and the numbers, they themselves are really important pollinators. And then their larvae eat a lot of the crops, the pests of the crops. So they're a double whammy when it comes to it, like baby bees do nothing, but baby flies are out there working themselves silly to help with

our ecosystem services. I mean, that's just the hoverflies. So what else do flies do that's really useful for us? Oh, well, hold on. That's the hoverflies are pollinators. About half the species of flies are pollinators. Okay. And this includes things like mosquitoes. So people are like, oh, no, mosquito's all bad. No, really important pollinators. In the Arctic zone, there's about 4,000 scribe species of fly, insect. 2,000 of those are flies. And mosquitoes, because they can survive this really quite horrible environment,

really important pollinators. The midges, everyone hates. Yeah? There, the pollinators are chocolate. So if you get rid of bitches, yes, you get rid of chocolate, which I find amusing. So you've got all these different families doing pollination services

in quite extreme environments we don't necessarily think about. But then also they're predators. So they're getting rid of a lot of things that we don't like. They are recyclers. So the whole thing about flies hanging around feces and dead bodies, it's good. It's incredibly good because can you imagine if they didn't? Our environment would be, well, I think rather unpleasant. I think that's the nicest way of saying it. So we need them for decomposition. We need them for pollination. We need them for all these sorts of different ecosystem functions. I do find that quite surprising when you say that they're found in the Arctic because we generally think that insects can't really hack those really cold environments.

But if, you know, half the insects in the Arctic then flies, that's incredible. Well, you can find them 5,000 metres up mountains. I've collected flies from mountains in Peru and I can barely walk and they're like, wee, having fun. We've collected them at the base camp of the Himalayas, you know, base camp of Everest and things like that. We know they do that. But we've also collected them from the bottom of caves. We found them at one kilometer down underground. We found them in Antarctica. They're the largest purely terrestrial animal in Antarctica because the rest, yeah, think about the big ones. They're both. So purely terrestrial, it flies at three millimeters. You've got, they exist everywhere. And you get them in the sea as well.

and we don't think about insects in the sea, or most people don't, but there's actually hundreds of species of insect that's gone to the sea. When you say you can see insects at the seaside, what sort of things are we talking here, little sandflies and things like that? There's little sandflies, but there's little dollies, which is our reflection. There's a family called Dolly Capoday, so they're just sort of dollies. They're the best of flirts. So you can see them just the males, wing waving all the time, going,

hello ladies, and you can see the ladies ignoring them. So that's quite cute. But you get this family called Coronaidae, and then non-biting midges. And basically, this family have just packed a passport and have gone everywhere. So these are the ones that you can find in the desert. You can find in the Antarctic, Arctic, in the sea. You know, it's like, really? And they're like, hello, we're here again.

And they have an amazing physiology. They have more different types of globin than we do. so they can store oxygen as well as remove it around the body so they can live in really anoxic environment. So it's great. And there's one that's called the sleeping coronamid, and it does exactly that. It can desiccate its body to 3% of its original weight

and go to sleep for up to 13 years they found so far. What sort of lifespans do flies have? I mean, you think of the classic may fly, which people say only lives for about a day, but can some flies live for longer than that? Okay, so mayflies aren't flies, just to start off with. I know, it's the problem with common names. Right, dragon flies, definitely not a fly.

Horse flies, yes, annoyingly. And you can't see it, but when you write it, if it's one word, it's not a fly, and if it's two words, it is a fly. So there's that. Now, the lifestyle, we forget the larval stage. We always forget about the babies. I mean, we're terribly negligent.

To be fair, most flies forget about their offspring as well. But some of them can have a very short turnover. So some of them can be a week. And these are the species that exist in like ephemeral habitats. So they've got to say a feces, you know, a dead body. They've got to get in there. They've got to reproduce fast. They've got to do that.

That's how rapidly they can turn over. But as I said, some can live up 13 years. So it really does depend on what they're feeding on and in the environmental conditions. And some of them can east of them. eight, i.e. they can, what, they go through a summer hibernation, and some of them will go through winter hibernation. So all sorts of different life cycles and strategies depend on what they are. And you said they go through a winter hibernation. Is that where all the flies go in the winter? Because you're in the summer all saying, oh, this flies everywhere, and then winter comes

around and they're gone. They do everything. So some of them will overwinter as adults. We generally get we. I'm not a fly. I've got to stop saying we. A lot of the males die out because they're quite pointless. So a lot of them, the females, was overwinter as adults. But there are a group of flies called Clusterflies. And I think you can see what they do. And they all basically huddle up together and go to sleep. And then in spring, I know it's rather cute, but we always get loads of people going,

oh no, there's loads of flies just coming out. And it's like, mate, they're fine. They're going out. They eat wood lice and things like that. So they're not interested in us at all. They've just snuggled down and hunked down for the winter. But then a lot will overwinter as eggs. or a larval stage and do that.

So it's a good stage to be in. That's what will happen to them. So which parts of the world will have the most fly diversity? Well, classically, it's the tropics because you've got huge amount of variation, speciation. They didn't get the big glaciation periods, so you still have this rapid species evolution going on. But it's not, I mean, that's great,

and it's lovely seeing those. But actually, some of the less. diverse habitats as well offer some of the more interesting species and some of the weirdest species because they've had to adapt. So, you know, like the Arctic. So yes, it's going to be species depoporate, but it's got some crazy adaptations going on. And the way that the plants and like the flowers and the species of insects have evolved alongside each other has created some marbles. Saying that, though, South Africa and the Cape of South Africa, because of the floristic diversity there, you've got some stunners, some absolutely amazing flies

there. What's the weirdest one you've seen or you know of? There's one that's got a mouth part, which is the insect is about two centimetres long and its mouth part is a further six centimetres long. So that's quite amazing. That's the equivalent of you having a six metre long tongue, which I think is quite cool. Something like that. I worked out weird proportions. But then you've got all sorts of things. There's loads of stalked fly. So they grow their eyes on the end of stalks. And this has happened, this has evolved independently 22 times. So they love it. But some of them also have antlers.

They've got an or they've got protusions out of their cheeks. Some of them have flags on their bums. A lot of them have tickling apparatus. Yeah, I know. Actually, a lot of their genitalia is quite extraordinary. But there's loads of like ones that you would come across day. in your garden, there's a whole troop of hoverflies whose larvae, I affectionately call the bum-breatvers, and they have these raptails, which is basically an elongated siphon,

that's an abdominal siphon that they breathe out of, hence the bum-breatzers. And these are telescopic, so they can go from like, you know, a one-centimeter-long maggot could suddenly become two or three centimetres as it expands its little breathing spiritual. And that enables it to dig down in whatever's disgusting that it wants to eat, but still breathe from the surface air. Like snorkeling. Exactly. They are literally bog snorkeling, which is great. Now, how smarter flies? They've evolved all these crazy things, but how intelligent are they? Well, we're beginning to, we've mapped their neurological pathways now. So they've done a map of the brain. There's 100,000 neurons, I believe. And they're beginning to look at

how they process. And they do learn. So we are seeing this. We're beginning to process, but they did some horrible experiments, cutting limbs off to see, I know, to see how they would act. So they, for example, they always wash with their first pair of legs and they cut their first pair of legs off. And it took them a little while, then they realized, so they had to clean with their second pairs of legs. So they're doing all sorts of things like that, recognition, things like that. So they are, it's just terrible behaviour of things. So they're shocking the larval stage and the adult stage will still remember to avoid these sorts of like things.

And it's like, oh, the ethics are violent. But yeah, so we're beginning to kind of finally look at and understand their intelligence. Now, why is it so hard to swatterfly, though? Not that we should. No, no. You're only allowed to kill flies for science. That's my rule. Because they process so much quicker than we do.

So each of the large eyes is composed of a series of ometidia. So imagine these ometidium as an individual photo unit. So they may have up to 5,000 plus of these photo units. Now, in all other insects, that photo unit is this fused tube of what originally consisted of eight photo cells, so six black and white two-color. But in flies, those have defused, as it were, and they've gone back to individual photo units, apart from the two-color, seven, eight are still fused. And so when it takes an image, it takes an image from six different parts.

So it's able to get a greater acuity than most other insects with a number of omitidia. So, you know, you've got 636,000 images being taken in one go. Its neurological pathway is really fast, okay? And it often bypasses the brain and just goes an impulse straight to the wings. So it's able to kind of move so much faster. So you appear like a slow motion. It's like being in the matrix, you know, you're like, oh, you want neo or the fly is neo. It's just going to what is going on here?

So if you do want to catch a fly, just go very slowly because then it won't process that you've got movement going on. And then catch it nicely and put it outside. Exactly, exactly. Now, we tend to think of flies as carrying diseases, but how many flies or what percentage of flies are actually dangerous for humans? Oh, very, very small. The actual percentage is. And they are vectors, that's absolutely right. and I'm not going to negate how important they are as vectors, but they themselves, they're just being manipulated, this is what I would say.

So we are looking at a lot of the sanguivores, the blood feeding species. So the mosquitoes obviously are number one. But within that family, there's 3,500 species of mosquitoes. Only about 150 of those are important vectors, of which 20 are like the big ones. So when you're talking like absolute numbers, there's very few species of flies that are important in the 165,000. So we have to be mindful not to say all flies. That's like saying, blaming all mammals based on our behaviour, you know. So there's definitely things that we need to consider.

And I don't think we should eradicate mosquitoes because I think they're too important. but we definitely need to think about breaking transmission barriers and doing things like that. And what's about things like house flies, because they'll sort of land on disgusting things and then stamp all over your food, is that not actually a too big of problem? No, no. I mean, it's not really. I mean, I'm very, so they will, they can do mechanical transfer, but we do worse. Never look at money because they did some examination of what's on money and it is

really quite disgusting. Or peanuts in a bar. Don't ever eat those, just saying. So yes, anything can be in a mechanical transfer. And because they're attracted in, of course, this can happen. So I would say, cover things up. Just be logical. Flies don't understand home ownership and where and where they can't go. Okay. So it's not like they understand this. In fact, you've kind of built your house on their habitat. So this is why they were coming and do that. without realizing it, humans are really filthy. We absolutely stink. And so they're like, well, of course I'm going to come in.

You smell fantastic and I'm going to try and eat your food. So yeah, cover up food, put things away, try and make things not as attracted to them. Houseflies, though, are really important pollinators. Yeah, we are starting to think about how we can use them. For example, they're really good at pollinated and bell peppers in greenhouses. Really? Yeah. That's the whole thing about flies. You can't say that they just do one thing because it's like, hold on, they do multiple things. It's great. Now, I've talked about how important flies are. So what are some of the threats that flies are experiencing, things like climate change, pollution. Is that affecting them?

Yes, yes, yes, and yes. Everything. Everything. So you've got the original, you've got land use change. This is the biggest species last. You've got introduced species coming in that is taking over habitats. You've climate change. neonicotenoids, all of these things are having a massive impact on flies. And the problem we have is very little long-term data. Oddly enough, people haven't collected flies or recorded flies in maybe the same way they have done with birds and other things like that. We're beginning to build it up now. I mean, the UK is lovely. We have this UK organisation called the Ditchers Forum. And there's about 400 of us fly specialists and, you know, all walks and wide, going out there recording and figuring out. So we're providing long-term data sets to enable us to what's going on. And yes, they have seen declines.

They've seen declines in species that are in specialist habitats, feed on specialist things like that. Intensive agriculture has had a massive, massive impact. You know, they just haven't been able to live. Cocoa plantations, this is ironic because cocoa, will die out because they're losing the habitat where these fly pollinators live by building monocultures. So our lack of knowledge about what all the species are and what they do is causing us a problem now. Is there anything people can do in their gardens or if they've got even just a window box that can help the flies? First off, my advice is to do nothing. I love this. I don't like

the word messy because that implies that it's anything wrong. But a little bit wild, let something go, you know. We forget about the larval stage. And the larval stage, obviously we've been talking about is so important. So if you can in your garden put in a pond. And this is beneficial. There's some brilliant stuff going on. It's not just beneficial for all the insects. You got all the amphibians coming back because they're feeding on insects. You get the birds coming back because they're the feeding on the insects. So you have this massive, not. You have this massive non-examining. You have. on effect by looking after little insects. But if you've only got a window still, plants, potty plants, they need that. Ivy is the best thing ever. Ivy, and this is what I love, it's,

it's a, you know, you just let it grow because it is an autumn, winter and pollinating plant. So it is really, if you go out now and you're just going to have a look, the ivy is covered with insects and it's great. So just, just relax. Try not to use as many bad products. just be a little bit less tidy about things, and they would come. Now, insects and particularly fruit flies are really important in science experiments. They're used a lot by scientists. You know, they've even been up on the International Space Station. So what is it about fruit flies that makes them so very useful for science experiments?

Well, it's a little bit of an accident, how the fruit fly got picked in the first place. So it did happen. It was there. It was successful. It was in the lab. You know, it was the classic thing. And they were using lots of hairs before. And hair's quite big.

Yep. Not so easy to use in lab conditions. Take a long time to reproduce, whatever. You've got these little flies. They're feeding on bananas. They are reproducing like nobody's business and they're free, basically. So suddenly we were able to start our technology, our understanding of how to look at genes and to manipulate genes.

To be fair, it took them quite a while with the flies as well. But, you know, we were like, okay, this is great. And so that's it. We learned how to manipulate the faster. Now, it could have been any fly. And if there was talk, it should have been like black, dark wing fungus gnats rather than Josophilome melanogaster. And so it's not necessarily the fly itself.

And this fly is slightly weird as well. I mean, it does a lot of things that we're like, hold on, that doesn't happen in other flies. So, but it is still, it's got so. many inherited diseases that are the genes that are the same as ours. We can understand the behaviour. We can understand its physiology and we can, you know, extrapolate with ours as well. It's such a useful little model. It's brilliant. I like the flat. We get these flies drunk because it's not ethical to get humans drunk. It's just like, I could volunteer for that. How'd you get them drunk? Do you just give them a bit of alcohol like you were with humans? Well, the Drosophila,

They're not fruit flies, which is a thing we have to kind of like, their real common name is vinegar flies. So they're attracted to that, you know, when fruit has gone off. And this is why you get a lot of drunk flies because they are flying around. And there's some brilliant genes associated with making flies, like flies and alcohol, which we have as well. One's a cheap date gene. And you've got all of these. So we're looking at our own susceptibility to alcohol by looking at these genes.

And so, yes, and they do, this might sound familiar. When the flies get drunk, the males start walking around, then they start falling on their backs. And they just like legs in the air. And then they become very amorous, which their ability to choose, their partners just completely disintegrates. So they're just, it's like, yeah, it does sound. awfully familiar when you put it like that. I mean, obviously, because I work here, I work on

not just living flies, but we have this amazing historic collection. And the collection goes back 350 years. It's great. And we're now, I really do think we're now, although we've got to hurry up and describe things, okay, we're running out of time. And we've been, as a species, we are horrendous. And I'm quite selfish as a member of the species that I'd like it to survive. So I like this planet and I'd like, you know, my friends and family to decide. And so one of the things we've got to do is rapidly describe, but we've got to rapidly understand how evolution is happening, how these different things are impacting on everything. So I have quite a few different projects going. And one of them is working with the Welcome Sanger Institute. And it's historic DNA recovery,

which is a great thing. And we've been able to do this with lots of things now. But my, because I work with a collection. I don't want it destroyed. It's our biological heritage. And with a lot of these projects, it was, you know, you'd take a leg. And I know insects have got six, but we're like, come on, back off. So we've been washing them with various different buffers to extract their DNA. And we've been very successful. So we're getting whole genome DNA from material that's 100 years old without damaging the specimens at all. So this is great. So we've been able to see

when the gene for insecticide resistance first appeared in a museum collection specimens, which is good. Can you imagine the sorts of things we can't start looking at? We've also looked at the blood mills in the mosquitoes, and we've been able to identify which plasmodium they've been transmitting. So again, there's all sorts of questions we can ask from our collections. We can see which plasmodium started coming into which species went.

We can understand how they spread. We can understand all sorts of things associated with collection. And that's just those. Think about what we could start doing then if we look to the pollen of the insect collection, in their guts around their mouth parts. We can truly tell you which flies are pollinating what. So it's just like, I just need someone to give me, I don't know, 10 million.

That's all I'm asking. and I would go, and we will just sequence and we will go through the collection and get all this information. Thank you for listening to this episode of Instant Genius. That was Fly Expert, Dr Erica McAllister. The latest issue of BBC Science Focus magazine is out now. Pick up a copy and store or visit sciencefocus.com. This podcast is sponsored by name, audio and focal.

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