A Tour Of The World’s Weird And Wonderful Flies

29:27 minutes

You may be most familiar with the flies that hover around your fruit basket or kitchen. But some of these insects have the most unusual lifestyles on Earth. There are the “thuggish” robber flies, capable of killing hummingbirds; the delicate and nearly invisible midges that pollinate cocoa plants; and an assortment of bot flies that can live under human skin, inhabit the stomachs of rhinos, or dwell in the nasal cavities of reindeer. Erica McAlister, senior curator at the Natural History Museum in London, affectionately refers to these flies as ‘snotbots.’

[Meet the glittery jewels of the bee world.]

In her new book The Secret Life of Flies, McAlister takes us into the world of Diptera and the extended fly family. She joins Ira to describe these flies and more, and tells of a close encounter with a human botfly.  

Read an excerpt of McAlister’s book here, and view photos of these fascinating flies below.

Bumblebee robber fly
The bumblebee robber fly, Laphria flava, quite possibly my favourite fly, with a hardened proboscis for penetrating prey, often through the eye. Credit: courtesy Firefly Books
a small tan bat fly
The rather odd-looking Mystacinobia zelandica, the New Zealand bat fly, with claws on the end of their feet to grip on to and move through the hair of bats, their hosts. Credit: courtesy Firefly Books
stalk-eyed fly
The most impressive of all stalk-eyed flies, Achias rothschildi. When the adult emerges from the pupa it swallows air and pumps it through to inflate its own eyes. Credit: courtesy Firefly Books

Segment Guests

Erica McAlister

Erica McAlister is a senior curator at the Natural History Museum in London. She’s also the author of The Secret Life of Flies (Firefly Books Ltd.).

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, we’ll raise a toast to the new year and test your whiskey science smarts. Do you know the chemistry behind that oaky vanilla flavor? Do you have the details on distillation? We’ll talk about it. But first, I’m sure this sound–


–makes us squirm. Right?


Ah! Got it! But wait, my next guest would prefer that you think twice before swatting. Her new book is The Secret Life of Flies. And it’s a love letter to the beautiful flies, the unusual flies, to the deadly and destructive, and, yes, the disgusting members of the extended fly family. And the book is filled with surprises. I didn’t know a whole lot of stuff about flies.

For example, did you know that without a certain type of pollinating fly you could kiss your chocolate bar goodbye? And yes, I did say pollinating fly. Flies do pollinate. Who knew that? Or that pesky mosquitoes are technically flies, too. And yes, even mosquitoes have a purpose in the world, contrary to what you might think.

Erica McAlister is the author of The Secret Life of Flies. She’s the curator of Diptera at the Natural History Museum in London. She joins us from the BBC. Welcome to Science Friday, Erica.

ERICA MCALISTER: Hello. Thank you for having me.

IRA FLATOW: We won’t be taking your calls today, but check out the pictures of some of these incredible flies. You can see them at sciencefriday.com/flies. I had no idea that flies were so interesting. When did you discover your love affair with flies?

ERICA MCALISTER: I’ve always loved insects and I’ve generally been an outdoor– and I’m small and I fall over a lot. So I do spend a lot of time just observing the little things, but it really wasn’t until my PhD. And then afterwards I started getting to explore the flies.

And then once you start, you realize there’s just no going back because every time you think you’ve got them sauced, another one comes along and goes, ha ha. And you’re like, aw really? So they’re the most diverse. They’re the funniest. They’re the most intricate. They get everywhere. They do everything. There’s just no point looking at anything else.

IRA FLATOW: You talk about how important flies are for pollinating. I had no idea flies were pollinators.

ERICA MCALISTER: No one does this. I mean, I think poor flies have got the worst press on the planet. Most people don’t even realize what a fly is. They just try and kill them without thinking about it. And it’s like, I don’t go in your house and kill your puppies. Don’t go out and kill the flies.

And of the families described, we think half of them are pollinators. And unlike the bees– the bees don’t like the cold– but the flies, they get everywhere. They’re up in the mountains. I’ve collected them at 5,000 meters. They live in the Arctic, the Antarctic. They just get everywhere. They’re so important as pollinators.

IRA FLATOW: Yeah. Let me remind our audience that they can check out pictures of some of these incredible flies at sciencefriday.com/flies. These aren’t your standard houseflies we’re going to be talking about. But you do talk about your standard housefly.

ERICA MCALISTER: Yeah, I mean, I feel sorry for the housefly. I mean, it’s our fault for being quite revolting at times. It’s latched on to us as an obvious species and it’s just followed us around the world. I mean, we get houseflies in the base camp of Everest now because we’re just such filthy individuals leaving our trash everywhere. But the houseflies are one family of like 150 families.

So that body form that everyone thinks of, it’s not usual in comparison to [INAUDIBLE] flies because they’re all so weirdly different. It’s just–

IRA FLATOW: Yeah. Yeah. I didn’t know that until I saw and you have wonderful color plates in the book showing off the flies close up.

ERICA MCALISTER: The whole thing is that I’m describing things and everyone’s like, nah, it’s not fly. And I’m like, no, trust me, it is a fly. Even the flies without wings, which is like, is that not a walk? No, it’s still a fly. And they are just amazing. And they’ve just taken this body form and just gone with it. Some of them will rip their wings off midlife. The larvae are so different to the adults anyway. So the bit that we know is the flying around bit. That can be a day. That’s it.


ERICA MCALISTER: Most of their lifecycle is the eating phase which is quite nice way of living your life.

IRA FLATOW: Let’s talk about it in a little bit, but I first want to talk about this surprising fact. I learned it about the chocolate. That flies are necessary for cacao pollination, but their habitat is also being destroyed.

ERICA MCALISTER: Yeah. Ironically, I hate chocolate. I just think it’s revolting, which I think is why me as a crusade for this fly is quite funny. But the adults, they have a specific habitat they want to breed in. And the female, she lays her larvae in aquatic environments. Now our insatiable appetite for this revolting substance has caused us to knock down forests where they naturally occur in to build all these monocultures of chocolate.

Now the chocolate is pretty much like a panda, pretty bad reproductive rights naturally anyway. So if you suddenly get rid of the flies, then their reproductive rates are going to be crashing completely down. So you have whole habitats, whole monocultures of this plant that’s just not producing any fruit, any of the seeds.

IRA FLATOW: So we could be losing our chocolate?

ERICA MCALISTER: Yep. Yep. See? You don’t look after the flies, you lose chocolate.

IRA FLATOW: You wouldn’t care about that though as you say.

ERICA MCALISTER: No, but I like the flies. The irony about these flies as well is that it’s from the family of biting midges. So the things that you hate when you go up north and to the wild wetlands of Alaska and things like that, and they plague you mercifully. These are the ones. The males are the pollinators.

IRA FLATOW: Sometimes they call them no-see-ums.

ERICA MCALISTER: No-see-ums, Sands exactly. And they have to be no-see-ums because the cocoa plant is so complicated to get through to its reproductive parts. The fly is minute to be able to get through.

IRA FLATOW: Wow. Wow. So the pollinating role really is highly unappreciated and unknown.

ERICA MCALISTER: Yeah, I mean, we’re beginning to look at it now. There’s lots of studies in hoverflies looking at pollinators. But it’s just we see thousands of flies flying around plants, but no one takes attention because they’re not the bees. So it’s probably massively underrated what’s going on with them.

IRA FLATOW: Now I know that over the years we’ve talked about some very famous plants, that when they bloom, they smell really like rotten meat. And I didn’t really understand that reason and you talk about it in the book is that this is what attracts the flies.

ERICA MCALISTER: Yeah. And I’ve now sampled off one of those plants. And I’ve sampled in a lot of bad habitats in my life, and they really do stink. And the thing is that they are attracting the flies that like corpses, rotting bodies, et cetera, the decomposing flies. And these things are getting those in there and they’re trapping them inside them to cover them with pollen till they’re ready to be released again. And they will go and find another decomposing smelling flower. Yeah.

IRA FLATOW: Wow. You know, I didn’t realize until I read the book also that mosquitoes are part of the fly family.

ERICA MCALISTER: I realized I’ve failed, or we have failed, is that my mom asked me this when she read the book. She was like, oh, I didn’t realize mosquitoes are flies. And I was like, well, what did you think they were? And she was like, oh, well, I hadn’t really thought about it. And I think that’s my whole problem with flies is that no one does think about it. I mean, we barely think of them as animals. And that’s the whole thing. Yeah, I mean, crane flies– I hate the common name because it means three different things. But the flying daddy long legs, those are flies. All your midges are flies. They’re all– there’s hundreds of thousands of fly species out there.

IRA FLATOW: So they really make up a large part of the animal kingdom.

ERICA MCALISTER: Yes. Off the top big four of insects, they’re in there with the beetles, the butterflies, the bees and wasps, and the flies. So and then when we start to properly look at them– thanks to new genetic ways of looking at our species– I think we’re going to have a bit of a shock to actually realize how many species of flies are out there.

IRA FLATOW: Now there are also lots of predatory flies, too.

ERICA MCALISTER: They’re my babies. I love them. There’s a group I absolutely adore and they’re the robber flies. And again, this is something we don’t think about is flies being venomous. So everyone thinks about the bees and the wasps and the ants. And it’s like, most of the predators in the flies– and things like mosquitoes– are actually injecting little bits of venom. And one of those groups is the robber flies. I think you call them assassin flies.

And these are some of the top aerial predators out. In fact there’s a species in Southern California that has been shown to catch hummingbirds on the wing, which you just think the idea of this thug of a fly coming along, there’s somebody watching this tiny pretty little hummingbird. It’s come along. It’s caught the hummingbird. It’s paralyzed it and it’s shredded it completely. It’s quite fantastic.

IRA FLATOW: This is one on one? Or is it a whole group of flies?

ERICA MCALISTER: No, one on one. And we’ve got them in the collection. They’ve caught dragonflies. They are such good aerial predators. And they can take– it’s terrible, I shouldn’t know– they can do quite bad damage to hives of bees, et cetera. Because they’re just thugs of flies.

IRA FLATOW: Wow, and there are parasitic flies, too.

ERICA MCALISTER: Yeah. There’s some amazing Endo- and ectoparasites. And just the adaptation these flies have had to go through to live in the house that they do or in their host is quite– this time of year, everyone’s going on about the reindeer and Santa and it’s like, well, there’s the snot bots. So there’s the little parasitic larva that lives down the nostrils of a reindeer, which isn’t maybe so nice for the reindeer, but it’s how this fly has evolved for its larvae to live there. It’s quite fantastic.

IRA FLATOW: And you make that point in the book is that during the life of a fly, it’s really the larvae that do most of the damage because they’re very hungry.

ERICA MCALISTER: Yeah, And they have got no other function basically apart from to eat. So they’ve got no sex organs. They’ve got basically no mechanism for movement. They are purely just there to eat. And some of them would survive like up to five years just eating.

IRA FLATOW: And they might live inside another animal doing that?

ERICA MCALISTER: Yeah. There is a little parasitic group of flies called the Acroceridae, or the hunchback flies, and these live in the insides of spiders and the abdomens of spiders. And if they get into a spider that’s too immature– because the spider is going to, again, live up to five years– what they would do after they would eat some of the less vital organs, and they basically just go to sleep for a couple of years and wake up when the spider is mature enough for them to eat the rest of it.



IRA FLATOW: Well, we’ve seen horror movies about insects crawling into people’s heads and depositing eggs in whatever. Is that possible with flies? Can they get inside people and–

ERICA MCALISTER: Well, yeah, we’ve got the human botfly. So I’ve not had this yet, but it’s amazing. It’s in Central and South America. They’re really big and beautiful with massive eyes and quite clumsy flies and quite noisy fliers. So they figured out to catch either a horse fly or a mosquito. And then they lay their larvae, or eggs, on the underside of these mosquitoes.

And so when the mosquito flies along, when she starts feeding on you, at that point, the butterfly will drop onto your skin and crawl through the hole. It’s quite fantastic. And they will spend a couple of weeks just munching away underneath your skin so you can see them and hear them at night.

IRA FLATOW: Can you do anything about them?

ERICA MCALISTER: Well, you can get rid of them.


ERICA MCALISTER: But, I mean, they don’t do any real damage.

IRA FLATOW: Oh, they don’t?

ERICA MCALISTER: Well, it depends what you call real damage.

IRA FLATOW: I guess, yeah.

ERICA MCALISTER: In the greater scheme– scare of things, it’s not really a problem.

IRA FLATOW: Erica McAlister, author of The Secret Life of Flies. We’re going to take a break and come back and talk lots more with her, so don’t fly away. We’ll be right back after this break.

This is Science Friday, and I’m Ira Flatow. We’re taking a world tour through the fascinating realm of flies with my guest Erica McAlister, author of The Secret Life of Flies. You mention in the book that you turned down the opportunity to actually have a fly travel through– was it your system?

ERICA MCALISTER: I, sadly, haven’t had a botfly. One of my good friends has had one. And sadly for me, he wouldn’t let it rear out. So after about a week or so, he was like, Erica, and swore at me a lot and said, if you don’t remove this thing from my head. Because it was on the head, it couldn’t go down. It had to go along the cranium. So you could really watch it develop. And he was like, no, this has to come out. And so we were in the jungle.

There’s nothing I could really do, so I’ve just stacked Vaseline over the top to suffocate him because they breathe out of their anal spiracles So they breathe out of their bum. So you could see these little spiracles waving around. So you suffocate them and then I anesthetized him with half a bottle of rum, which I thought was very generous. And then I slightly cut open its head to be able to extract the larvae out of it. But, yeah, it’s in the collection now, which is good.

IRA FLATOW: And you enjoyed every second of it, I’m sure.

ERICA MCALISTER: Of course I did. I’m a scientist. No, it was fascinating stuff.

IRA FLATOW: Oh, there’s so much to talk about. We’re talking with Erica McAlister, author of The Secret Life of Flies. Let me tell you, this is one eye-opening book. Beautifully done, I must say, Dr. McAlister.


IRA FLATOW: And you make the point that flies– we’ve ignored their biodiversity studies. We study all kinds of things. We don’t study flies!

ERICA MCALISTER: No, I mean, flies are very difficult. If you look at the age in the UK of the great Victorian hunters and everyone goes on about the [INAUDIBLE], the beetles, and the amazing butterflies. And it’s because, actually, they’re quite easy to identify in many ways. Butterflies, you’ve got obvious patterns on the wings that are quite easy. Flies, tiny black flies is quite a common theme across all of them.

And a lot of the identification is on genitalia dissections, which is quite fiddly. And obviously you need a lot of things like microscopes, et cetera. So a lot of people just ignored them. And then where they are the most biodiverse, their larval stage, they basically just resemble sleeping bags full of vegetable soup. There’s very few features about them, so everyone just goes, ugh. And then just goes, yeah, there’s a lot of fly larvae and that’s it. And that tells us nothing.

IRA FLATOW: Oh, that’s it’s an incredible.

ERICA MCALISTER: I know, I mean, imagine doing a habitat survey of birds and said, you’re right, they’re all pigeons. And that is basically what we’re saying.

IRA FLATOW: Let’s talk about maggots. I mean, you’re so fascinated with maggots. I know that.

ERICA MCALISTER: I mean, it’s the whole compartmentalization. We think about how clever the human is and now we adapt into being these humans. And it’s like, yeah, but they go through four complete life stages. And each one is specifically adapted and has adaptations within that as well. it’s just I think that utterly fascinating.

IRA FLATOW: You talk about how necessary it is to have maggots for the disposal of waste. And also people are experimenting with them as a feed for livestock. Tell us. Wow.

ERICA MCALISTER: Well, I mean, the black soldier fly is the classic one here which it’s an amazing– it’s a ubiquitous. It’s now basically found all over the world. And we have maggots farms rearing up this little fly. And the thing about maggots is they’re so protein-rich. Absolutely incredible. They’re little packages of omega-3. They’re just absolutely amazing things. And unlike a lot of the other protein that we get, they’re not extravagant on water and they don’t use up so many of the other resources.

And the thing that maggots don’t do that cows do do is maggots don’t pass wind. So this is a massive impact on our environment. So we are now, instead of like trolling the seas and using all of these products to feed our livestock, we are actually using these maggots to feed the chickens, pigs, et cetera. And what’s really cool about these maggots is that we are feeding them to the livestock.

And then when the livestock defecate, we’re feeding the feces back to the maggots. So there’s this beautiful little circle whereas they’re not only providing food as they’re getting rid of waste. So basically everyone is benefiting, apart from probably the flies that are doing all the work and getting none of the benefit.

IRA FLATOW: Do you think there is some– how shall I put it? Human food, some day down the road eating maggots?

ERICA MCALISTER: Well, without you realizing that you’re eating any already– there’s a lot of, yeah. I mean, you just think about in chocolate, you’re eating whole bits of insect, but that’s another story. Yes, I think we will. I mean, obviously we’re going to not have maggots that have been fed off feces or dead bodies. But we are going to start producing that. Just the housefly larvae maggot is so protein-rich and so available.

And the idea of us growing them in factories that are not on such a horrible substrate, so we can break them down. And the nice thing is now we’re thinking about because– ugh, it’s only the Western world that really has an issue with this. But because we’re so fussy about what our food looks like, we’re producing lots more insect flour. So you can start breaking it up and putting it into food so you’re not realizing necessarily what you’re eating or it’s not causing you to be so squeamish about it.

IRA FLATOW: I have to go back to that chocolate comment you made about we’re eating– that’s for another time. Hey, now is another time.

ERICA MCALISTER: OK, well, it’s just you’re allowed. The governments all around the world allow so many insects to be in your products. Apparently, the biggest one– and I love this– is frozen cauliflower. It has more insects in it than anything else. The next time you have any frozen cauliflower, just have a little look and you can probably find aphids and all sorts of things.

And the same with chocolate when they’re making it, you get lots– and you can have whole parts of insects as well. I mean, I wouldn’t know because I’ve never really– the last time I had chocolate was too many years ago for me to pay attention. But, yeah, all of our products. You know, I go and feel we’re in the middle of nowhere. So the rice I’m eating is probably completely covered with insects. It’s not a problem.

IRA FLATOW: Hm. “Flies love alcoholic drinks,” you write in your book.

ERICA MCALISTER: Yes. Well there’s certain groups particularly known for them and we are utilizing these for our own advantage. The fruit fly, Drosophila melanogaster, which has been our classic lab model for hundreds of years. And we’ve looked at the genetics and everything. But naturally, this fly has a tendency to eat rotten fruit. Rotten fruit makes alcohol, and it’s quite fascinating. We’re now looking at this fly and we’re getting this fly purposefully drunk so we can look at the impact of alcohol on genes. Because their genetic makeup is so similar to ours, it’s very useful.

Because apparently, ethically, we’re not really meant to get humans drunk. So we’re taking this advantage. And they’re very much like humans. When the males get drunk, they become more amorous and then their ability to carry out their functionality as it were decreases quite dramatically. So it’s quite interesting what’s going on.

IRA FLATOW: So the fly mind is willing, but the flesh is weak.


IRA FLATOW: And of course we know that flies– and you talk about this– feed on poop! We have a picture of a bunch of dung flies hitching a ride on a dung beetle.

ERICA MCALISTER: Yes. I know. I love the fact that there’s so many different types of flies associated with different types of dung. And there’s a wombat fly that eats wombat poo and things like that. And they are very important, because if you imagine if it weren’t for the flies getting rid of all these feces, we would be– as I say, we’d be swimming around in a quagmire of the stuff. And that is, I don’t think, a particularly pleasant thought for anyone.

IRA FLATOW: Do you think people should go out and do what you do and sit around a cow pie or a dung poo and have a watch about what’s going on there?

ERICA MCALISTER: Do you know what? Yes. I mean, maybe you don’t have to start off on a dung pat. I could say start off on a bush. Anything. But just have a watch, because flies are also very flirtatious. And there’s a lot of mating rituals going on. So you can watch and observe the males dancing for the ladies. They’re either throwing their legs up in the air, some of them have got paddles, doing all these sorts of things.

Some of them have got very pretty wings, and they’re trying to dance, doing all these intricate behavioral traits. And that’s an area that we’ve only just started looking at because their life as adults is so short that often we never catch them as the adults. So definitely go out and start observing all these things that are going on.

IRA FLATOW: In the book, you talk about flies with magical healing properties that go back centuries that we knew about. Tell us about that.

ERICA MCALISTER: Well, before the advent of penicillin, we were very concerned about what to do. And in fact, let’s go back even further. Genghis Khan realized that there was something about these group of flies that was very useful. As he went marauding across Asia, he always took a cartload of maggots– these [INAUDIBLE]. And basically, they are used for removing gangrenous flesh. And at the same time of removing this rotten awful flesh, they’re also secreting enzymes, which not only is stimulating to skin to bind properly again, it’s reducing infection rates.

So come forward to now, and the last century, we used to have– I love the fact that in Yorkshire, there was a maggotorium where some guy, Arthur, used to go to the local zoo. And every time an elephant died, he would take the corpse off to the woods and let it decompose. So when these maggots got in, he was able to scrape them out and he put them in their maggotorium. And these fine Victorian ladies would sit there, inhaling the fumes, which I have to say, that probably is quite smelly. But it reduced things like coughing and we are now seeing– we’re looking at it– it does have an impact on TB and things like that.

So nowadays, and again during the American Civil War, that was when we did so much advances because they were realizing– there were many doctors who were making notes observing– that when a maggot infestation in a wound actually cleared it and there was less chance of getting gangrene. So today with increased infections, penicillin resistance, increased infections, and also things like type 2 diabetes, the level of gangrene in hospitals, et cetera, has gone up dramatically.

So we’re now producing these maggot bags. And so we’re once more utilizing these maggots there again. There’s massive factories producing these maggot bags to actually cover over our wounds for them to actually eat it, this decomposing, this really nasty rotten flesh.

IRA FLATOW: You said they’re sort of like teabags. They put the maggots in the bag and they can–

ERICA MCALISTER: Yeah, because apparently we don’t like seeing maggots crawling around. So for sensitivity reasons, they now come in what looks like a teabag. So you put them on your wound and then you wrap your wound up. And then after this is checked regularly by the nurse, and then it’s removed. And the maggots are sterile maggots anyway. They’ve come from a very clean environment. And then after they’ve done their bit, they get sadly destroyed. It’s not like they’re released to have their freedom afterwards. But, yeah. So the entire process is incredibly sterile and very, very beneficial.

IRA FLATOW: There’s a chapter on the so-called “vegetarian flies” in your book, which sounds a lot better than the poop-eaters eaters or the dead body eaters. But you say they’re actually some of the worst agricultural pests, yeah?

ERICA MCALISTER: Yeah, well this is it. People don’t think about the vegetarians being really bad for the planet. I mean, they come in number two after the caterpillars. I mean, caterpillars are out there marauding and everyone forgives them when they become butterflies. However, the flies don’t have that luxury. They’re hated as larvae and adults. So some of the biggest, most important problems come under the fruit flies and the vinegar flies. So these are ones effecting olives and carrots and all of these crops that are so important to us in many ways.

IRA FLATOW: In case you’re just joining us, we’re talking with Erica McAlister, author of The Secret Life of Flies This is Science Friday from PRI, Public Radio International. Now I can’t let you go with that because we are a science program– to talk about how important flies are for scientific research.

ERICA MCALISTER: Huge. You name it. They’re there. They were the first animals into space. They are one of the most ubiquitous species. They occur in marine environments, terrestrial [INAUDIBLE], arboreal, below ground. They live in the Arctic. They live in the Antarctic. They live in– the great news recently about was finally figuring out how the diving flies of the Mono Lake in California. This has a pH of 10.


ERICA MCALISTER: Exactly. These flies are so amazingly adaptive. It is so important we look at them, understand them, and we can use them to understand so many other things about the habitat, food security, vectors, the environment, modern medicine, everything. They are vital.

IRA FLATOW: Let me see if I can conclude with talking about bat flies.

ERICA MCALISTER: Oh, I love bat flies.

IRA FLATOW: Being really weird. Tell us what you love about them.

ERICA MCALISTER: Well, they’re just so weird. Now there’s quite a few families of bat flies, so which one do you want? Do you want the terrible hairy?

IRA FLATOW: [INAUDIBLE]. Tell us about both of them.

ERICA MCALISTER: Well, the terrible hairy fly was this enigma. You know everyone goes on about endangered species. Well, the terrible hairy fly has being found from one location, and it was first discovered in the 1930s. When they went back in the 1940s, and then it wasn’t discovered again until a couple of years ago. So this is arguably one of the most endangered species on the planet, and yet it’s not even in IUCN. No one is worrying about it apart from a handful of dedicated fly specialists.

And the thing about this fly is it lives on a crevice of a cave of a mountain with one colony of bats. And for years, we didn’t know what was going on. Was it feeding on the bats? Was it feeding on their poo? What was going on? And now, thanks to this last collection that’ve gone back, they’ve been able to look at it’s got contents and realize it’s feeding on the feces. So it’s actually living a very nice and very beneficial life with these bats as well.

But the weirdest thing about it is it looks like a tiny spider that’s lost a pair of legs. It’s got tiny, tiny wings. It’s orange. It’s fluffy as anything. It’s like a very long-legged teddy bear. It’s an incredibly looking thing and no one puts it as a fly.

IRA FLATOW: What about the fly that actually gives birth to live young and lactating glands?

ERICA MCALISTER: Yeah. These ones are found everywhere. These are amazing creatures. There’s a whole superfamily, as we call it, Hippoboscoidea, that contain these flies– the things that you hate– the tsetse flies, but also the incredible bat fly. And these are found all over the world. And these are amazing because the females give birth to live young. So we think this is like a prerogative of high vertebrates, but some higher invertebrates obviously do this as well.

Internally, she has lactating glands on the inside. She has milk glands and she raises her larvae inside. So the egg hatches internally and then she feeds the larvae for up to a week before giving birth. And these larvae changing body side a hundredfold. I mean, can you imagine?


ERICA MCALISTER: Yeah, think about a human with that sort of situation going. Most of her body is her offspring. It’s quite fantastic.

IRA FLATOW: Speaking of fantastic, so is the book The Secret Life of Flies by my guest Erica McAlister. It’s an amazing book. I mean, it opened my eyes to the whole world of flies that I knew nothing about. And I’m sure our listeners will see the love affair that you’re having with flies in that book. Thank you very much–


IRA FLATOW: –for being our guest and taking time to talk with us today.


IRA FLATOW: Erica McAlister, as I say, author of The Secret Life of Flies, curator of Diptera at the Natural History Museum in London.

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Meet the Producer

About Christopher Intagliata

Christopher Intagliata was Science Friday’s senior producer. He once served as a prop in an optical illusion and speaks passable Ira Flatowese.

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