For the Love of Flies: The Unsung Heroes of the Insect World

Flies are amazing insects that play critical roles in our environment including pollination, waste disposal, pest control, and as a link in the food web. Flies are greatly diverse in colors, shape, size, and where they live. Butterflies and bees probably generate more enthusiasm, but it’s time to change that. 

To talk about flies with us, we are joined by Dr. Erica McAlister, who works at the Natural History Museum in London, where she is the principal curator for Diptera and Siphonaptera, i.e., flies and fleas. Erica takes a particular interest in three groups of flies, fungus gnats, assassin flies, and mosquitoes. The latter means that inevitably she is involved with many projects related to identification of mosquitoes and which ones are associated with spread of malaria and other diseases and viruses, but her experience is much broader, including teaching entomology in Dominica and studying the invertebrates — more specifically, the flies — of that island. Finally, Erica is also the award-winning author of four books, including The Secret Life of Flies and The Inside Out of Flies.

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Cover Photo: Whitney Cranshaw - Bugwood CC - Tachinid fly (Trichopoda pennipes) 

Thank you for listening! For more information go to xerces.org/bugbanter.

Transcript

Rachel: Welcome to Bug Banter with the Xerces Society where we explore the world of invertebrates and discover how to help these extraordinary animals. If you want to support our work go to xerces.org/donate.

Matthew: Hi, I'm Matthew Shepherd in Portland, Oregon.

Rachel: And I'm Rachel Dunham in Missoula, Montana.

Matthew: Flies are amazing insects that play critical roles in our environment including pollination, waste disposal, pest control, and as a link in the food web. Flies are greatly diverse in colors, shape, size, and where they live. Butterflies and bees probably generate more enthusiasm, but it’s time to change that.

Matthew: To talk about flies with us, we are joined by Dr. Erica McAlister, who works at the Natural History Museum in London, where she is the principal curator for Diptera and Siphonaptera, i.e., flies and fleas. Erica takes a particular interest in three groups of flies, fungus gnats, assassin flies, and mosquitoes. The latter means that she inevitably is involved with many projects related to identification of mosquitoes and which ones are associated with spread of malaria and other diseases and viruses. But her experience is much broader, including teaching entomology in Dominica and studying the invertebrates—more specifically, the flies—of that island. Finally, Erica is also the award-winning author of four books, including The Secret Life of Flies and The Inside Out of Flies.

Matthew: Welcome Erica!

Erica: Thank you for having me.

Matthew: Of course. So before we get into questions, I want to talk about names. And that's because, you know, you and I are British, Rachel is American. I've been in the U.S. for 25 years or more, so this is a topic that I've bumped into a number of times. And already in the introduction we mentioned assassin flies, and so some American listeners might be going, “Well, what's an assassin fly?” And that's kind of what sparked me wanting to insert this. Because assassin flies—I look up in the index of the U.S. field guide and I don't find them—only assassin bugs—but that doesn't mean they don't exist here.

Erica: I thought assassins was an American name. We call them robber flies.

Matthew: Oh, because we call them robber flies here, too.

Erica: Yeah, no. So there’s a—. You have some of the world's experts on assassin flies—Torsten Dikow in Smithsonian. And he's got the assassin fly website, and he loves—. And we call them robber flies, so we have the robber fly recording scheme, which is quite cool. I don't know which one I prefer because both of them are quite good at conferring the predatory nature—.

Matthew: Yeah, it describes what they do. Yeah.

Erica: Yeah, I mean, they both—they rob life, they steal life, they do all sorts of amazing things. They're highly venomous flies.

Matthew: They kill.

Erica: Yeah, but, you know, so do a lot of things. But that is nature. It's not Disney. So yes, we have those that are different names. Then we have the hover flies, or you call them, or they're known as flower flies.

Matthew: Or syrphids, yeah.

Erica: Yeah, syrphids I prefer, because I think of—because that's on their Latin name, Syrphidae—and I think of them surfing across the air. So as you see them hovering in your garden, I just think of them surfing. And I think that's a nice—. When I learned all my scientific names, I would sit there in my head thinking of all these different ways to remember them. And I still can't now say syrphids without kind of just striking a little pose.

Matthew: Haha.

Erica: But this is why we should use scientific names, not common names. Because then it's meant to be a universal language we can all understand. I mean, just for example, in the UK for woodlice—.

Matthew: Oh, woodlice.

Erica: Yeah, there's loads and loads and loads of common names for woodlice depending on where you are in the UK. And they're all little cloak or little like folk names for them, which is like—it gets very confusing just in the UK. Can you imagine globally? When you’re trying to have a conversation.

Matthew: Yeah, totally. I have a copy of the Bugs Britannica book here by Richard Mabey and Peter Marren, I think.

Erica: Yes, yes.

Matthew: And that lists loads and loads of names for the woodlice, so yeah. It’s awesome.

Erica: Haha.

Rachel: All right well we're going to jump into our questions and we're going to start with the basics. We haven't talked about flies, really, on our podcast yet, and I'm really excited to cover this topic. Very excited to have you here. So we refer to flies as Diptera—what does that name mean?

Erica: So Diptera—di-ptera. “Di” is two. “Ptera”—as the P-T-E-R-A—is the wing. So it's the two wings. And this is in reference to a typical—I won't say all—a typical adult fly. So it's meant to be one of the diagnostic features of that order. The other being a suctorial mouthpart. So you cannot be bitten by a fly. You can be like pierced, and maimed, and shredded, and all sorts of fun things like that, but not actually bitten, because they don't have a man—they don't have a jaw, as such. And then they have one of the most phenomenally exciting things is this pair of halteres. Now they are not unique with having halteres. We see it obviously in the twisted-wing parasites, the Strepsiptera, and we see it in some, bugs as well. So some coccids, and things like that, they have a pair of halters. And these though, mean—are the most amazing proprioceptors. They're the balancing organs, they're the gyroscopic—you know, they enable them to have some of the most phenomenal flight patterns on the planet.

Erica: And these little flies, they're little jump jets, you know, they're hoverers—they do all sorts of things. They can zoom in upside down. I mean, just landing upside down on the ceiling—oh, I've got that silly song in my head now—but it's just a phenomenal feat. And we don't give them enough credit. I mean, I can barely coordinate, as I've got a sprained ankle, right, basically walking along the flat ground and they're operating in this three-dimensional space, and you're like, “Wow!” So they are so good at what they're doing. But in saying those three things that make it a fly, there's lots of flies that don't have mouthparts, there's flies that don't have wings, and there's some flies that don't have halteres. So they're very good at taking that basic blueprint and laughing at it, and going, “Do you know what, evolution? Let's see what I can do next.” So they're highly adaptable both in morphology and behavior and many other things.

Rachel: I love that. So flies are obviously a very diverse group of insects.

Erica: You’re sounding English now. You've got two other English people—.

Rachel: Haha. I didn't even mean to do that.

Erica: You’ve gone West Country on us, lass.

Rachel: Haha. And they're actually one of the most diverse orders. So how many species are there?

Erica: They're not the best described yet. We are—I think, it's about—the recent—I got told recently, I think we're up to 185,000. So we are very lucky to have an amazing community of dipterists around the world. And we have the International Dipterists Society now, and we have all sorts of things, and everyone is working to try and sort out the list of names and clean it up. So it's not the biggest—Coleoptera, or beetles, has about 400,000. But us—I describe myself as a fly. I've got to stop one day doing that—us and Hymenoptera are in what has been termed the “dark taxa,” which I love it because it has leanings towards fantasy realms. And it's basically because there's a lot of stuff out there, and a lot of small stuff, but it's very cryptic. We don't know what species there are, etc. So estimates with flies. Real numbers—we are a lot higher than what we thought.

Erica: There was a shocking paper that came out of Canada that estimated in the millions with one family, Cecidomyiidae, which is the tiny gall midges. They're the ones, they’re the ones that we all go, “Oh God, it cecids. They all look alike.” And there's one or two ardent fans going, “No, they don't! They don't! Trust me.” And the rest of us are like, “I think they do.” But they estimated 1.8 million species within that one family of fly. And yes, your face is exactly—. We were like, “Oh, dear. Nope.” But there's a lot more out there. They're very diverse.

Rachel: So you talk about small. I think we've probably all seen like the classic black fly that's flying around our food, or maybe us if we don't smell very good. But when you talk about tiny, like how small is the tiniest fly and what is that comparable to?

Erica: Oh, the tiniest fly is a phorid. Horrid phorid, I affectionately call them. Sorry Brian Brown, in Museum of Los Angeles, who is like the prince of them. It is very small. I mean very small, like less than a full stop. These flies, I call them horrid phorid because they're really easy to get to family. Really distinct venation on their wings—when they have them—but when you get to species level there are issues when it comes to taxonomy. But Brian Brown, you need to look up some—. He's described the smallest flies in the world. And one of them, he's named after Arnold Schwarzenegger because it has got really muscly legs, which is quite cute. Haha. I'm sure Arnie loves that.

Rachel: Oh, that's great. Haha. So can you find flies all over the world? Are there areas where there are fewer flies, more flies?

Erica: I like flies because they basically get their tarsi into every little habitat you can come across. They are really, really good at doing that. So we talk about the largest purely terrestrial animal in the Arctic is a fly at a whopping three millimeters. “Whoa.” They are—oh, sorry, Antarctic—in the Arctic, as well. They're everywhere. In fact, of the 4,000 species in the Arctic, I think 2,000 are flies—they love a nice bit of freezing. They're in the deserts, they’re in caves, they're in the deepest lakes of the world. They love saline environments, so you've got the Mono Lakes of California—they're in there. I was very lucky to go and collect some flies from the tar pits, the La Brea Tar Pits, which was amazing. Flies living in petroleum, I mean, come on. They’re just doing it.

Erica: And there's flies in space because we've sent them up there, and they've been living in little colonies in space. You think, “Yeah, come on.” And there's marine flies. There's some beautiful—. Chironomids are a family of flies. They're the non-biting midges. And I describe these as the explorers, because they are basically the ones who've gone, “Let's try it out.” So they're in the Antarctic, the Arctic, the mountains, the bottom of lakes, in the sea. And some of them live in the desert, and they are—there's one species known as the sleeping chironomid, where it can—if the time's bad, it just goes to sleep for 13 years! 13 years of sleeping. I mean, why do we bother as humans? Amazing things.

Rachel: Wow, that's incredible. So for folks that are listening that may be sort of new to IDing different insects, you know, bees and flies can sometimes look somewhat similar. What's kind of the easy way to tell them apart? And is there an easy way to tell them apart?

Erica: They fly differently. So bees, and bumbles—the humble bumbles, etc.—they kind of loop more. Flies have got a little bit more purpose. They're like, “Move across, bees. We've got things to do. We've got attitude. We're going to do it.” Obviously at rest, it's the two pairs of wings, rather than the four pairs of wings. Although I admit that to be quite difficult. Generally, the antennae are different. Hymenoptera generally have bowed antennae—I'm going to tell you there's loads of flies that have that, as well. Bees, I don't often see—. So solitary bees are generally if they're not feeding, they're not there. Where flies, we often see resting in many places. And they are definitely checking you out. I love the way everyone thinks that all flies are plotting because they're always doing that, you know, and they're like, “Oh, what is going on?” This is not plotting, although I like to believe some are. It’s that they have to keep themselves ultra clean. They are exceptionally clean animals. They have a huge sensory apparatus on their head—where most of the insects do—and they have to always keep this clean. So that's why they look like they're planning the overthrow of the government.

Matthew: I like that. What you were just saying about them being ultra clean, because so often we associate flies with dirt.

Erica: Yeah.

Matthew: You know, which just seems like pretty bad rep that they've got.

Erica: No, I'm not going to lie. I mean, there's a lot of flies that do like that, but disproportionately they don't. So a lot of—and, no offense—a lot of the time you're seeing the flies is because they're in a human-induced environment, and we are, we are filthy. Rachel, you were saying earlier, you do smell, and I don't mean this personally, but I mean, the pair of you absolutely stink. They can, they have exceptionally—. Haha. I love telling people this. “No, we don't.” “Oh, you really do, trust me.” Even dead, you know, they can smell a corpse on a really good day up to nine kilometers away. Can you imagine what a living, breathing human smells like then? And we create these environments. We leave food out, we have—we are surrounded by our own wastes, and decomposing material, and all sorts of things. So of course they're going to come. And because a lot of their larvae live in these environments, they have to make sure that they don't get any bacterial infections.

Erica: I told you I was going to go off piece. Here we go again. So maggots—they're looking at the antibacterial properties of maggots because they can live in feces, or dead flesh, and things like that—and it kind of looks like they're covered with loads of like microvilli, and this causes or prevents the bacteria from managing to get to them. So we're thinking of developing like pills and medicine coated with a similar property, as in the structure, so we can send them into environments, so they don't get—just don't get destroyed by bacteria. So I love the fact that we've looked at these animals living in these weird, filthy environments and thought, “How can we understand that and utilize it for our own good?”

Matthew: Yeah, I knew that maggots were being used for keeping wounds clean.

Erica: I know.

Matthew: But not gone, not thought further as to, well, why can they live in, why can they survive in those places?

Erica: And I love this because it's now getting other disciplines looking at our environment. It's not just entomologists going, “That's amazing!” It's actually having like physicists, and medics, and biochemists going, “Now, why is that amazing?”

Matthew: A lot of that leads us into, I mean, natural history of flies. You know, 185,000 species, maybe 1.8 million. Haha. I mean, there must be so many different kind of life histories behind that for, you know, egg laying, and feeding, and finding shelter and habitat. I mean, is there such a thing, kind of a typical life history for flies?

Erica: The flies—I’ll give you typical—but flies, as I've already said, they don't really stick to their blue plan. So there's the egg, the larval stage, in which there may be a number of instars depending on what species it is. And then like many, or most of the animals on the planet, I should say, they through a complete metamorphosis. So then they go through this pupil stage. And then there's the adult. Now this is where it gets fun. Because all of that depends on what you are. And some of them don't even do that, which is like, “Ugh.” There's a whole group, a whole infraorder of flies that give birth to live young. So they properly get pregnant. They have lactating glands on the inside, so she suckles her larvae internally. I mean, the idea that these little flies being properly pregnant little mothers. And she gives birth—. Like this—examples as the tsetse, and you've got the bat flies, and the bird flies. And sometimes they can give birth to something that has a mass greater than them, which is why she will only give birth to maybe up to three in her lifetime, because you wouldn't want to go through that.

Erica: Whereas you've got others which—I've gone for the opposite. So they're terrible mothers. Some of them will have weaponized ovipositors, so she basically has a submachine gun that she fires off thousands of eggs around the garden and just abandons them. So she's the, you know—she's gone from really caring to, “You know what, good luck.” And then within some of these, like the spider-killing flies or the hunchback flies—I think you can tell what they look like and where they live with that name—and then the bee flies—these are parasitoids. So the mother lays—well, “lays.” She hurls out thousands of eggs—and the larvae then goes through two different types of form, which is great. They change from this planarian which is this like, it's like, you know, it's the toddler stage of the human life cycle. It's very active, it's trying to get as fast as possible, you've no idea where it's going, because it has to get to its host. And often its host is underground—it will try and find it as quickly as possible. And then it reverts to a second form, which is like the teenager. [It] becomes like this big slob, and just sits with its host, consuming it, and just lying there. And honestly, its form is just beautifully globular, and things like that. “Ahh, I'm just going to eat and eat.” And then, you know, once it finished feeding—may take a while—it then migrates back out of this nest, and pupates and these beautiful fluffy or hunchback adults appear.

Erica: So you get a lot of variety. Some of them are amazing. So sarcophagids—these are the flesh flies—their larvae feed on carrion. And any animal that has an ephemeral food source, they have to be ready to act immediately. So you think about things that live in dead bodies, or anything like that, decomposing material. They're out there, they've got to do it. So she can change, depending on what the food environment is, from laying eggs to laying larvae. And they dissected mature females, and they've got larvae all the way up to their ovaries. Can you imagine, perhaps, that writhing mass inside you? Haha. I just love flies. So you've got all these—. And then you've got—I mean, where do I even start? Metamorphosis, the pupil stage, is a phenomenal thing.

Erica: And a lot of flies—this is what we consider inactive. But then you've got things like mosquitoes, that the pupa is active. You know, these beautiful tumblers, as they're knocking up and down the water column. It's something Bobert described it as, “A beautiful thing watching these things going up and down.” And it truly is. But you've also got ones within the pupa, they have a puparium. So the higher flies, they have this extra case. And they have basically an airbag on their head. That once they're ready to get out from the puparium, they burst their head. So it's literally, they blow the doors off—if any Michael Caine fans are out there. “You blow off the bloody doors,” as it’s said in the film—and then you can watch them afterwards as they like hatch from this puparium, and their heads are like, “Woo, woo, woo, woo.” And as they're engulfing more air, this collapses, their wings expand, their body takes form from this dull gray to this beautiful metallic sheen, maybe green or blue, as in the blue bottles. And it's just a phenomenal zing seeing that.

Erica: And most of the flies, the larval stage is in completely different habitat to the adult stage, so there's no competition. It's not like baby bees that just stay at home and get looked after by the aunties. You know, these ones are out there, they're doing stuff, they're contributing to the world society, I'm telling you. And they, you know—. So there's no competition between these two, which has enabled them to be so phenomenally successful.

Matthew: Wow.

Erica: Sorry, I get a bit excited. Haha.

Matthew: No, no. Bug Banter is totally the place to do that, you know.

Erica: What I love about flies, as well, is that you can see all of this in your garden, or in a plant pot. You know, we don't have to travel to see such phenomenally amazing things. The metamorphosis, the idea of reorganizing most of your body tissue. I mean, come on, humans are so dull. You've got this like, “I'm going to basically spend most of my life cycle eating,”—which I think we should all take heed to and think that's a really good thing—then we change our body form, and then we just, the next bit is just a tiny bit of reproduction, and that's it. How fantastic? No taxes.

Matthew: I was going to ask whether there are any kind of distinctive or unusual life histories you could tell us about. Haha. You've already done that, but if there's any others—just because this is so fascinating to listen in.

Erica: Yeah, okay, I’ll tell my favorite bat fly. And this is a—it's a bat fly that—and there’s a lot of flies that when they copulate, the female will rip her wings off, okay. So those phorids I talked about earlier, so some of them are coffin flies. So I think you figure out their habitat. So they will copulated in midair, and the males just drop them little like mother torpedoes going down, and they will bury down to the corpse in which they lay their eggs. But there's some other bat flies, that when she gets pregnant—and she's on a bat—she will stick her head in the bat—because she's feeding off them—but she also rips off her wings, and then her legs, and then evaginates her abdomen over her body entirely. And it’s like, “What, hold on a minute. Why?” And the really lovely thing is, if you look at the anal spiracles, or if you look at the spiracles of flies, they kind of do look like little faces. So it’s like this giant button face on the side of a bat and you're like, “That's really a fly.” So it looks like a flare—er, sorry—a pear with a little stamp on its bottom. It's just weird.

Erica: But it’s like, how do these evolve? You know, like how do bot flies evolve? How did it evolve that this, the reindeer bot fly—the mother squirts her maggots into the nostrils of this reindeer? I mean—. Or, or, talking of bot flies—as we do. The Dermatobia hominis, the human bot fly, which is—of course, we've named it after us, but we came along lately. So this was a bot fly of large mammals in central South America, and then we came along and we were everywhere, so they were like, “Why not?” Now, a bot fly, I don't know if you've ever seen them, they're quite big and chunky. They're quite amazing, but they're also—we can hear them, so quite cumbersome things. So the bot flies, the Dermatobia, what it does is it catches another fly that will take the risky business of getting its baby to a host. So for example, for us, it catches mosquitoes, and horse flies, but it's also on fanids and masses and things like that, which are attracted to the other large ruminants. So we have them in the collection in the museum, little mosquitoes, with like eggs of the bot fly on it—she's stuck to the side. And then when the mosquito comes to us, the change in body temperature causes them to hatch and then fall into us. How cool is that? Haha. I love evolution.

Matthew: I know. It's just amazing that they can bring another species into their own life cycle.

Erica: Manipulative. Told you—can't trust a fly.

Rachel: I could listen to you talk about flies for ages.

Erica: Haha.

Rachel: It's so interesting. I am muted while you're talking, but I've been laughing this whole time and just truly amazed about flies. They're really these unsung chameleons of the insect and animal kingdom. I mean, it's really incredible. I'm just incredibly impressed. And I love how you talk about them. It's really great. I wish we could sit here all day and just have you tell us stories about flies. Haha.

Erica: I'm really lucky where I work. So I meet daily visitors from all around the world who tell me about the particular type of fly they love. And you can't help but be amazed, A, by the flies and B, by the people researching them, as well. Because these are their passions, and it’s—. I find it really, I find it still disheartening that we're still looking at flies in one way, when—. I mean, can you imagine if we based all mammals on us, and how dull we would find that, you know. All birds based on a robin, or, you know, something like that. And we do this, we lump it, and we consider ourselves, you know, as lovers of nature. And I meet so many people who are like, “Well, I love nature. Oh, I don’t like flies.” You’re like, “Oh.” But you've just written off a huge chunk of nature, a massive chunk of nature. And it's like, and they get up to—they're so diverse.

Erica: And they're morphologically diverse. There's a load of stalk-eyed flies. You know, these—they headbutt each other. I mean, come on. And they form little territories, and they lek. And often they will do all sorts of things, you know, they've got—some of them have grown antlers outside of their cheeks. There's dolichopodids that have little flags on their abdomen. “Hello!” Some of them have these reversible glands—the other, the male will stick his head in—it's very rude, I have to say. You know, Drosophila, they have these sex cones on their front legs—they stroke the lady. There's a group of Sepsidae, which are the scavenger flies, the lesser dung flies—a whole lab in Singapore was dedicated to studying their flirty behavior—I think that's how I should describe it here. And these flies kiss each other. It's just kind of, you know, come on. There's a lot going on with them.

Rachel: Oh, definitely. So aside from just being super cool and very interesting, why should we care about flies?

Erica: So A, I hate that question, because we should just like animals anyway.

Rachel: I agree.

Erica: But if we were to break it down to ecological functions, well, basically, we wouldn't really survive without them. So everybody knows the bees as the pollinators—eh, which isn't quite the case in many an environment. So a lot of the social bees—and we're going to get rid of, let's get rid of honey bees straight off, okay? They're a farmyard animal. Yeah, I'm happy. We're ditching them, yeah. They're not part of this ecological conversation. And anyway, honey bees have got a short tongue, and so they're not adapted to a lot of the plants. But that's another point—I'm going to stop going on about honey bees. Apparently, I'm too taxist when it comes to the bees, and I must refrain from being. But flies actually were pollinators of gymnosperms. So even before the angiosperm radiation happened and all the flowering plants, the flies were there pollinating. They're really important pollinators. And unlike many of the bees, because they don't live in the same social structure, they don't go home at night, or go home to feed their larvae, their offspring, so they're doing more feeding visiting events. They are messy feeders. Bees have their nice little pollen baskets and everything's oh so cute—whatever. Flies—all over their faces, right? Pollen is just everywhere. You need to check out mosquitoes flying around with massive lumps of pollen on them. It's just quite incredible to see. And in doing so, they're really good at transferring. So they may not be able to take as much pollen in one event, but because of their activity, they're transferring loads there.

Erica: Only really just beginning to look at these pollinating things. In the arctic, they've been doing lots of pollinator studies, and yep, it's the flies doing all the—most of the pollination. And they are able to survive in very harsh environments, all sorts of things going on there. And the pollinators in the Arctic, the big ones are the house flies. So, you know, we think about—if we were to think about flies being important pollinators, we'd think about the hover flies, and they are exceptionally good pollinators, and I'll get on to those in a minute. But mosquitoes are really good pollinators.

Erica: And the ceratopogonids, those biting midges, seem to have taken a very, very good liking to my partner, who's very upset right now with my flies, although none of them have attacked me. It's like they know I'm here. They're like, “I'm going to leave her alone.” Those biting midges, they are the pollinators of chocolate. So you've got chocolate, pollinators of coffee, carrots, mangos, all sorts of things—some of the primary pollinators are flies. Because they're so, they're so adaptable in their morphology. So cocoa, for example, I describe as the panda of the plant world. It’s generally useless [at] fertilizing, okay, and like producing fruits, as well, which is what most people are interested in. It's really basic, and really small, so it needs these tiny little flies to be able to maneuver itself around with inside these flowers.

Erica: Hover flies—these are great. And what we've been looking at recently—there's some amazing work on migratory hover flies. So some work that have come out of the UK, University of Plymouth, and places like that, looking at these flies that have come over from Iraq, Iran, Sub-Saharan Africa to come to the UK. So three generations of hover flies. And a lot of these are polyphagous, you know, they're pollinating all sorts of different things, spreading a lot of pollen. They're quite high, so they're able to see relic populations, so they're enabling gene flow to occur across these environments. Three generations getting here, so the little things are dying everywhere, which sounds terrible to them, but it's little nitrogen packages everywhere, so adding a lot to the soils.

Erica: And then when they get to the UK—and this is what I love about these immigrants—they get to the UK, and they mix with the local population. And the fecundity rate, if you mix these two populations, goes up enormously. And they produce little biological warfare packets—their larvae are aphidophagous, so they eat aphids. So they're controlling all—naturally controlling—all the pests of our crops, and our gardens, etc. So everything about these pollinators is superb.

Erica: I love the fact that there's some orchids that have caught on to this—and I don't trust orchids as far as I can throw them. They're the sneakiest plants around—and they release—so a lot of them will release a sexual pheromone that says to the male hover flies, “Hey, ladies here.” But there's some others that release a distressed aphid pheromone. These mothers will come down and lay their eggs there because they're like, “Oh, it's a good habitat for our little larvae,” will pollinate the orchid. And then being manipulated, just lots of manipulation going. So exceptionally important pollinators. Just think about the species richness and think about the abundance. We talked about house flies, but there's some calliphorids, the blue bottles, blow flies—we're looking at them in greenhouses as pollinators for bell peppers. So you name it, they're doing all sorts of things.

Rachel: That's amazing. Yeah, they're so important. And yeah, I think that question is slightly obnoxious because, you know, we should all just care about all animals, because we should.

Erica: But the thing about them is that even if the adults are pollinators, the larvae are generally doing a different thing—they're decomposers, they're predators, they're parasitoids. So one of the hover flies, you know, well, half of the family of hover flies in the subfamily Eristalinae, for example—their larvae are all basically hipsters. They're all recyclers. So they're decomposing, they're recycling our organic matter. And these are the ones that kind of a lot of them will look like—they're called rat-tailed maggots, which I call bog snorkelers, because they've got this—. Haha. I'm so the worst person for names, I'm really sorry. Haha. Next time, ask an adult person on. And they've got these anal spiracles—which is a great name—so there's this tubica, this very telescopic spiracle, which they will breathe from their bums. Breathe with your bums, eat with your mouth—much more sensible. And they're able to do this massive amount of recycling and then turn into these amazing pollinators. Like, other insects aren't like this. They don't have this bifold life cycle where they can be wonderful—both parts.

Matthew: That's great. No, and I really don't think we need to have an adult on. This is awesome.

Erica: Haha.

Rachel: I love the names, they're my favorite. Haha.

Erica: I just like the idea of these little animals bog snorkeling everywhere, just eating and bog snorkeling. And you can see it. If you go to the edge of the ponds, or in your compost—just rip apart your compost, you can see these creatures in there. And it's like, “Wow, this is really quite cool.” And a lot of them are very translucent, so you can actually see their gut contents. And you’re like, “Wow, that is recycling in my face.”

Matthew: Yeah, when you're talking about the bog snorkeling, and also the similarity between some flies and bees, I was trying to remember—was it Aristotle who thought that bees came from dead cows?

Erica: Yeah, yes. Yep.

Matthew: And that was because they'd seen the flower flies, the hover flies, come—you know, that had been bog snorkeling in carcasses. And they’d seen the adults coming out.

Erica: Yeah, it's exactly that. Because some of them are known for myiasis, which is any infestation caused by a fly. And they were in this carrion. I know—. I still find it amazing that 2,000 years on, we’re still quoting the same things, and that science has not like—. You know, maybe we’re just bad publicists, but it's like we really, really should be moving on from just these common misconceptions. I'm not having to go at you, but it's just.

Matthew: Yeah, but, no, but that was kind of my next question really was, I mean, what kind of misunderstandings do you think that people have about flies?

Erica: They're all dirty. And that's the number one thing. They're all disease carriers. Which is interesting, as we carry more diseases, but anyway. Yes, a lot of them are vectors. So a vector is they transmit all sorts of things from plasmodium, so malaria, to filariasis, little worms, as well as bacteria, and viruses. So right now I've just been to a mosquito control conference—that’s why I'm in Puerto Rico. Thank you, beautiful island of Puerto Rico—and we’re talking about all these things. Now there's 3,600 described species of mosquito, of which 50 of them are good vectors, of which maybe 20 are top vector. These mosquitoes, because of their feeding habits, they're the ones who've been manipulated, as well. So the malaria manipulates the mosquito. So one of my big misconceptions [is] that mosquitoes are the biggest killers on the planet. Well, no mosquito has ever killed a human. For mosquitoes to kill you, you would need 144,000 or something like that—I worked out on a piece of paper once—exsanguinating you at one time. And we just don't have that much skin for them to all land and feed. And, you know, if that was to happen, I think there's a lot of other things going badly wrong at the time.

Erica: And so, we need to kind of—. I feel that we need to move away from saying, “Look, let's try and stop—.” Maybe work on these 20 species—but what we do know is that malaria jumps quickly from species to species. It goes wrong. So let's think about how we can—maybe think about stopping that part of the transmission, rather than just trying to eradicate mosquitoes. Because eradicating mosquitoes feels very much like putting a plaster on it—or as you Americans call it, a Band-aid—on the situation. And we really need to think holistically of why these populations are becoming so prevalent, and why—. Is there a way we could do it without just trying to throw money at it, and do it in this kind of harmful way that we've generally done in the past, with lots and lots of chemicals? So I'd like us to think about that. And even if I was to talk about vectors as a whole, within the 185,000, we are still not talking a lot. There's, what, 6,500 species of mammals, of which one is a very, very destructive one. And I wonder, proportionally, are there more destructive mammals on the planet than there are flies? I don't know. But I think that's the way of looking at it.

Erica: So that's a misconception—that they're all bad. A misconception they're all filthy. A misconception they're all ugly. I’m sorry. If you've ever seen a bee fly, it just—that's just a lie, because they look like little fluffy flying narwhals. You know, they are, they're just 100% adorable and whatever. And even like little psychodids, these are the owl midges—or another word for them is drain flies, which is terrible—but half the family—the psychodids—half of them are psychodines, and the other half—which I understand, they're the vector carriers, so we can ignore those for this moment. But the psychodines, they look like little caped crusaders. You know, they've got these kind of really fluffy little wings and fluffy little bodies and they just walk around in a little compost going, “Huh. What am I doing?” And it's like they're permanently forgetting what they're doing, because they've got that like, “Huh,” slightly shocked walk the whole time. But if you look at them under a microscope—in fact, if you look at most flies under a microscope—it’s like, “Wow!”

Erica: Therevids, the stiletto flies, they're like the hipsters. You know, they've all got beards. Your robber flies, a lot of them have got moustaches. I mean, even the ladies. You've got to appreciate that as a woman of a certain age. They just—there's so much beauty in them that I think we need to just give them a chance.

Matthew: Yeah, my follow-up question would be, if you want—one thing you want people to remember about flies, what would it be? And I don't know if—is it the beauty of them? Or is it just—?

Erica: I’d go diversity. I mean, diversity in absolutely everything. In life cycle, in food, in habitat, in life history, in form, in absolutely anything—diversity, diversity. It's just—. Because I think one of the reasons I got into them is because I loved insects. I love the fact they dominate the world, and they do all these things. And I was an ecologist—I love the interactions, or whatever. And every time you'd go anywhere, there'd be like a fly go, “Ooo.” You'd be like, “Really? You're here as well?” “Yeah.” And so you want questions being answered, you’d look to the flies.

Matthew: Yeah. And amongst all that diversity, do you have a particular favorite?

Erica: Do you have children?

Matthew: Yeah.

Erica: Do you have more than one?

Matthew: Yeah.

Erica: And would you have to pick?

Matthew: Well, I've got a favorite son and a favorite daughter. Haha.

Erica: Ah, okay, you've got one of each. I have flies of the week. I'm actually wearing this lovely fly, this is a robber flyer. And I definitely have a soft spot for the larger brachycera. Oh, but… I, no, I can't. Because immediately I start thinking of one, I go on to another one. I mean, I just—. I quite like a braulid, which are the bee-riders. Just because they've got combs for feet, because they've got to hold on to the bee’s back. And also, they just look like little teddy bears when they're walking along. And the fact that they're like, they're kleptoparasites, they're not true parasites, and they just feed on the food around the bee’s mouth. Haha. It's just like they're like little personalized beard cleaners. And I just… No, can't pick. Not going to pick.

Rachel: Speaking of favorites, that was my favorite answer of that question, that you just can't answer it. And Matthew sounds like my dad because I have a brother, and he's always like, “You're my favorite daughter.” And I'm like, “Dad, I'm your only daughter.” He's like, “But still, you're my favorite daughter.” Haha.

Erica: Yeah, see, I'm one of three and I definitely know I am their favorite. I'm just going to say that now. Because they can't hear this, but I know it's true.

Rachel: Haha. Oh gosh, that is funny. So you—we have a couple of questions that we ask all of our guests. And you talked a little bit about sort of what caught your eye about flies when you were already studying insects, but what inspired you to study insects in the first place, and then leading onto this very interesting group?

Erica: I think it's because they are there. They are—. You know, if you want to know nature—. I mean, I grew up quite feral. Well, my parents raised me, and dragged me up feral, but they also gave me a microscope quite early on. So those two combinations. Plus we weren't—we didn't watch TV. So it was books, nature, and a microscope. And that seemed to be a heady combination of an awkward social childhood, but a fun adulthood with a vivid imagination. And nature has more imagination than me. And so looking at all these insects, I'm like, “Gah, just what's going on here?” So there's the Nosy Erica that loves it. And then it just honed it down. I studied ants in Australia and I vowed never to study ants again. Oh my God. It was just like, there's a lot of ants, a lot of the same ants—I was identifying them. I played around with beetles for a bit, and that was quite fun. But they’re all right. And then the flies just kind of like nestled their way in and said, “Have you thought about us?” It's like a group help for entomologists. And I was like, “I hadn’t really, although I have been paying attention to you,” and then suddenly I couldn't turn back. They kind of hooked me.

Matthew: And then our very last question. It’s: if you could see any bug in the wild—but, you know, broad, any kind of insect, invertebrate—what would it be?

Erica: Okay, in New Zealand, there's this fly which lives with bats. And this fly is a social fly—it lives in a community. And the older male flies will look after the larvae, and the larvae and the adults clean each other. And the male flies will guard the nest by, “Zzz,” like that works. Haha. But I would love to see something like that, something so—. And in fact, if I'm still in New Zealand—because there's a lot of crazy flies—I want to go and see the bioluminescent caves. And seeing all the predatory keroplatids that just eat their sisters and brothers, which I just think is hilarious—talk about our previous conversation. So yeah, I would like to see two examples of the flies being naturally weird.

Rachel: Well, Erica, this—my cheeks hurt from smiling so much—this has just been so wonderful. I have learned so much, and I'm so inspired. I think I feel like flies might be my new insect, my new favorite. Haha.

Erica: See!

Rachel: Haha.

Erica: They are wonderful.

Rachel: They really are. I just feel like you have such an amazing way to open this world that's so beautiful, that I think so many of us miss out on. So it's been such a pleasure. Thank you so much for inspiring us and sharing so much knowledge. We appreciate it.

Erica: Thank you. It was a pleasure. Thank you.

Matthew: Yeah, been really brilliant.

Matthew: Bug Banter is brought to you by the Xerces Society, a donor-based nonprofit that is working to protect insects and other invertebrates—the life that sustains us.

Matthew: If you’re already a donor, thank you so much. If you want to support our work go to xerces.org/donate. For information about this podcast and for show notes go to xerces.org/bugbanter.