Episode 28: Y’all Heard of the Picture-Winged Flies (Ulidiidae)?

Four images of one fly, Xanthacrona bipustulata, showing its head, habitus, thorax, and scutellum.

Image: Four images of Xanthacrona bipustulata. (Source: Charles Wallace)

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Charles 0:00
The term promiscuous is not uncommonly used in animal behavioural studies to describe individuals who have multiple mates, and multiple matings. And I don’t quite know how to get there, but I would love to say that I thought of a really funny joke about slut shaming insects. [intro music.]

Hello, this is Assigned Scientist at Bachelor’s. I’m Charles and I’m an entomologist.

Tessa 0:45
And I’m Tessa, and I’m an astrobiologist.

Charles 0:47
And today it’s just the two of us and we’re talking about the family of flies that I wrote my MS thesis on: Ulidiidae. I would like to begin asking you what you know about flies?

Tessa 1:00
I know the formal definition of flies is that they have one set of main wings. And then their secondary wings have evolved into these tiny well, relatively tiny little things called halteres that are basically like maneuvering surfaces. That’s why flies can, like, fly in circles and zig and zag everywhere. Oh, and they also have a metamorphic lifecycle of doing complete metamorphosis because they start out as maggots and then turn into flies. And that is the extent of my knowledge of flies.

Charles 1:29
I mean, beautiful. I did actually, in preparation for this episode, I was like, I want to be able to say with confidence why flies are such good fliers, because you’re correct – most winged insects have two sets of wings and flies are relatively unique in that there are only two orders of winged insects that have only one set of functional membranous wings that they use to fly. One of them is Diptera, or the true flies, which is literally di-ptera, two wings. And then the other one is Strepsiptera, which are the twisted wing parasites, which we talked about when we discussed the first four episodes of the third season of [Star Trek] Discovery, because we went on a long tangent in defense of parasites.

And so Strepsiptera also have only one set of membranous wings in the individuals that develop wings. But in Diptera, it’s the front set of wings that are still membranous and full, and then in Strepsiptera it is the back set of wings. We’re already getting into a phylogenetics tangent, but this is my… I edit this podcast and I can do what I want. There was remaining confusion over the placement of Strepsiptera relative to the other groups within insects because it was like, well, they have only two wings, like Diptera, but they don’t necessarily share a lot of other evolutionarily informative traits with them.

Tessa 2:53
Right, could be convergent evolution.

Charles 2:54
Yeah, and… it is. Because our best understanding now is that Strepsiptera are a sister group, ie they’re most closely related, to Coleoptera, which are the beetles.

So the article that I found was talking about how… there was a study a couple of years ago looking at whether… because we know that halteres are part of why flies are such spectacular aerialists and they have such incredible control in the air. This is why you’ve never been able to swat a housefly, and you never will. And also don’t because, you know, we’re all God’s children.

So they actually went in and it was a question of, is this a mechanical control where there’s muscularity in the thorax that connects the two of them? Or is it more, like, sensory, where the halteres are getting in a lot of like sensory information and then it is more of a neural connection. So they actually went in and disconnected the like muscles in that area and they found that there is definitely a mechanical connection there. So as the wings go up, the halteres go down, as the halteres go up, the wings go down and when they sort of disconnected all that it was kind of just… higgledy piggledy… chaos, although there are still a lot of remaining questions, obviously, because insects are infinitely complex.

[interstitial sound] I love flies, and here’s why: the thing that is so unappreciated about Diptera is that they do everything and by everything I mean everything. There are endoparasitic Diptera in for instance the botflies, which nuzzle inside of usually mammalian skin and spend out their larval stages eating flesh, it’s a great time. There are ectoparasitic Diptera in, for example, the Nycteribiidae, the bat flies. You know, there tsetse flies which are absolutely wild. They basically develop one maggot at a time and it once it slips its way out of the abdomen of the female, it is bigger than the abdomen. It is wild. It’s a little bit gross, but it’s also very cool. There are agricultural pests, because of course there are… there are urban pests, because you know, psychodids – you got gunky pipes, you’re gonna get drain flies.

They just do everything – they eat plants, they eat dung, they eat wood, they eat flesh … Sarcophagidae, iterally called the flesh flies… they’re endo parasites, they’re ecto parasites – Diptera can, and does, do it all. And people really just don’t appreciate the extreme morphological and ecological and behavioral diversity that is held within flies for probably a couple of reasons. One, people think that they’re gross, because they always land on their food epic next to the most dangerous, medically dangerous animal in the world, that mosquito does belong to Deborah. But even then most mosquitoes are just chilling, you know, living their lives and being a food source for bats. Do you want bats to die?

Tessa 5:59
No one wants bats to die. Bats are awesome.

Charles 6:01
That’s a great, I think part of the problem is that the ones that people do know about are either a nuisance, ie muscoids landing on picnic foods or mosquitoes biting people, and on a scale of minor annoyance in just an itchy mosquito bite to very high annoyance in dying from mosquito-vectored pathogens, which to be fair is a pretty negative experience. And then there are the ones that are really awesome, that are really, really cool and beautiful and diverse and fascinating and wonderful, are often difficult for people to see because they do tend to be quite small. I think diptera really need a huge PR push, and I would love to be that person but unfortunately I have dedicated my life to being the PR team for cockroaches instead, and they need me more.

Tessa 6:57
I agree.

Charles 6:58
They’re having a tougher time of it out there. So that is basically… that is my, my argument in favor, genuinely, I think that flies are very, very cool. And I wish people knew about them enough to be able to appreciate them as much as they deserve. And so going from very, very general, to much more specific, let’s talk about Ulidiidae. If I said “picture winged flies” to you would anything come to your mind?

Tessa 7:23
Oh, um, no,

Charles 7:24
Not unusual! These are pretty low profile group of flies, they have previously been known as Otitidae and Ortalidae, and they are commonly known… as in theoretically, this is their common name, as the “pictured-winged fly.” And the reason they have this name is that most of them have quite distinctly patterned pigmented wings, where if you think about a fly, you know, draw up a fly in your mind, probably its wings are very clear, just a clear, membranous wing, right?

Tessa 7:58

Charles 7:58
Well throw that image in the trash, because picture-winged flies generally have wings that have these sections that are in the wings that are pigmented and that these sections are often quite distinct to species or to genera, and they can also be individually diagnostic, i.e. there are some species which have such a distinctive pattern that you can look at the wing by itself and know definitely that it is that species. And they vary in complexity – some of them just have like one dot at the end of the wing, and then some of them have these very elaborate patterns. And some of them have mimicry.

Another thing that I wanted to get into is the placement of Ulidiidae on the sort of evolutionary tree of insects, and also flies. And I don’t want to get into this too deeply, because I don’t think that it will be interesting to most people as much as it is to me. Actually, I would love, Tessa, if you could give your idea of what phylogenetics is.

Tessa 8:54
So my understanding is phylogenetics is figuring out for different organisms, like how long in the past did they share a common ancestor? It’s basically, you know, building a family tree for species. And historically, this used to be done based off of like, comparative physiology, and you know, looking at fossils, or what have you. Nowadays, it’s largely done doing genetic comparisons.

Charles 9:20
Yeah. And, and people still do morphological stuff, but there is just, by sheer volume, there is probably much more molecular phylogenetics. And so the phylogenetic tree, ie the branching diagram that shows the evolutionary history of these different groups within flies, is interesting because it is basically a Matryoshka doll where the more specific and narrowly defined the group, the more speciose and diverse it is. Basically, let’s say that the the biggest doll is Diptera, and then you open that up, and there are all these other little flies just sort of randomly in there, and then the next doll is Brachycera, and then you open that up and there are all these little flies, but the doll is Schizophora, and then you pull off the top of Schizophora, and it’s getting a little bit more difficult because sometimes at the very internal, you know, the smallest dolls,

Tessa 10:13

Charles 10:14
They don’t come apart as easily. And then you open up Schizophora and then there are all these little flies in there, and there’s Calyptratae in the middle, which includes some of the most… another, one way that I was thinking about it when I was putting these notes together was, you have kind of the spectrum of flies, where the two kind of flies that most people are probably aware of represent these two extreme ends of the phylogeny – where you have mosquitoes, and you have, like, houseflies.

Tessa 10:45
Right, right. You know, if they look very, very, very different despite just having two wings.

Charles 10:48
They look very, very different. Yeah, mosquitoes are right at one of the first divergences, like, you have the granddaddy fly ancestor, and Culicomorpha, which includes Culicidae, which includes mosquitoes, is one of the first branches off from that. So like a very old old group of flies, very underived, very early, like, relatively close to the last common great granddaddy fly ancestor. And then you have houseflies which belong to Calyptratae there in that very small, most internal Matryoshka doll, right. And so Calyptratae I don’t want to get into too much, but calypters are basically are these big, like, white pads under the wings. And you can… you can usually tell a fly belongs to Calyptratae, because you look closely and you see these big white pads, but dump Calyptratae in the trash because Ulidiidae are acalyptrates, which just means that they are within the doll of Schizophora but they are in the, like, random flies stuffed in there around Calyptratae. Basically, acalyptrates are just a paraphyletic assemblage within Schizophora, and if you don’t know what that means, don’t sweat it. And so I want to just briefly say what defines Brachycera and what defines Schizophora, because they’re both pretty cool.

So Brachycera is like the big… [sighs] it sort of gets you to the point of like FLIES, of like what a lot of people probably associate with flies. So you have… Brachycera is really defined by having short antennae. So if you’ve ever looked closely at, like, a photo of a fly’s head, you have probably noticed that their antennae look a little bit weird. Or maybe you haven’t, because you don’t spend a lot of time looking at insect heads and you don’t have enough overall familiarity with them to know which ones look weird and which ones don’t.

Tessa 12:46
Come to think of it, yeah, I’m actually having trouble picturing what the antenna on a fly looks like because they don’t look like the antennae you would expect to see on you know, a butterfly or whatever.

Charles 12:59
Well, exactly. Butterflies have boring antennae, they’re just like… filamentous, whatever. I think we’ve talked about my grudge against butterflies before, and all apologies to Erin for my grudge against leps, but I’ll never stop and I’ll never apologize. Anyway, so Brachycera have the antennae that are called aristate, which basically just means they got like, it looks basically like a ball stuck to the front of their head, and then a little filament that comes off of it.

Tessa 13:29
Okay, okay, yeah. Now I know what you’re talking about.

Charles 13:31
Exactly. They’re very distinctive. They’re really the only insects that have these kinds of antennae. And it’s not all flies because if you look at… this is one of the things that you learn if you like take an introduction to insect identification course or something where Nematocera, which is a paraphyletic assemblage, which again, if you don’t know what it means, don’t sweat it. They have these, you know, longer antennae that have a bunch of different individual segments. So once you’re in Brachycera… Brachycera is also kind of the point where you get like, the maggot. Like the MAGGOT. You know what I mean? Like, it’s juicy, it’s white, it’s got very little morphological complexity. Maggots. Because here’s the thing. Here’s the real thing. I actually love mosquitoes. I think that mosquitoes… I don’t love when they bite me because they get very itchy, and I also don’t want to get, like, West Nile, you know what I mean?

Tessa 14:23

Charles 14:23
Which I think is reasonable. But I, they’re so… as immatures, they’re so cute. They’re so gosh darn cute.

Tessa 14:32
You know what, actually, yeah, I’ve seen like the nymphal stages, and they are cute.

Charles 14:37
They’re really cute. They sort of just like flip around in the water and they’re having a great time.

Tessa 14:41
They look a little bit like teeny tiny seahorses.

Charles 14:44
Yeah, they got these little spikes on effectively what is their butt that they stick up above the water so they can respire. And then when they pupate their pupae are also hilarious, because they’ve got these little like, trumpets at the top, that look like Shrek ears. They’re incredible. But you know, if you look at a mosquito larva, it does not… it’s not a maggot. It does not look like a maggot, plus it lives in water. But once you get to Brachycera you’re really getting into like maggot territory.

And then once you’re in Schizophora, you’re like, full steam ahead, I am a weird little white grubby thing that basically just has a mouth and some hole so I can breathe… on my butt. And that’s it. So yes. And so then once you get to Schizophora… Schizophora is… so you can tell that an insect that a fly belongs to Schizophora if you look at their head, if you look like face-on to there, because they have something called a ptilinal suture, because the pupae of, like, Schizophora look like weird little capsules. And what they do is that they have a structure called a ptilinum, which fills up with fluid and pops the cap of that pupa right off, it just pops it off. And then they like struggle their way out of the pupa. It’s great to watch and they you know, they inflate their wings, they harden up and then the ptilinum collapses back into their head and it leaves this very distinctive arch called the ptilinal suture. And that’s how you know something is Schizophora. I’ll link a video of this happening because it is incredible to watch. It’s great.

I have no emotional reaction to, like, the miracle of birth, because frankly… we’ve talked about this before, I think mammals are pretty gross.

Tessa 16:29

Charles 16:29
And I think viviparity was a mistake. But I think when I watch like a Schizophoran fly struggle its way out of that pupa and struggle out into life, I think I have the emotional response to that, that most people have to like a newborn baby, I love them. And so that is where we find Ulidiidae. And Ulidiidae belongs to a superfamily called Tephritoidea. Tephritoidea is named for the most sort of the glory hog of the tephritoides, ie the most speciose and the most economically important: Tephritidae. Tephritids are known as fruit flies, and this is confusing to people because… when I say fruit fly to you, what do you think of?

Tessa 17:15
You know, the teeny tiny one that everybody does genetic experiments on and buzzes around fruit that’s been left out.

Charles 17:23
Yes. Drosophila in Drosophilidae… and wrong! I set you up for that though, so don’t feel bad.

Tessa 17:29
Okay, yeah,I figured there was a trick.

Charles 17:32
Yes. Those are… well, I would say – to entomologists, we know those as vinegar flies, but we don’t know those as vinegar flies, we know them as Drosophilidae. This is the thing that I get about like common names for families that non-entomologists don’t actually talk about. Because we don’t, like… I don’t call ulidiids the “picture-winged flies,” as I call them ulidiids. I don’t call drosophilids “vinegar flies,” I call them drosophilids. You know what I mean?

Tessa 17:58

Charles 17:58
So I don’t know where these like, quote, unquote, common names are coming from, because they’re not common among non entomologists, and they’re not common among entomologists, right?

Tessa 18:07

Charles 18:08
So who knows, but tephritids are really the fruit flies, and tephritids are very economically important, because a lot of them are significant agricultural pest species. And a lot of the research that exists on ulidiids is unfortunately, in the, like, area of – here’s what it is, and here’s where it and then that’s it. I thought that we could start by talking about the most obvious point, which is their wings.

Tessa 18:39
Yep, they got pretty wings.

Charles 18:41
They got pretty wings. So there’s kind of two primary things to talk about. One is… one of the most obvious behaviors that ulidiids exhibit is wing waving. And they do all kinds of different wing displays. So there are species that will walk up and down plants sort of making a rowing motion with their wings. Then there are other species, the two members of Callopistromyia that are found, you can often see them, where you see them, holding their wings up at a direct 90 degree angle over their abdomen. And why do you think they do this?

Tessa 19:15
I would imagine it probably increases visibility because this sounds an awful lot like a mating display.

Charles 19:20
That’s a great guess. And the answer is, nobody knows.

Tessa 19:23
Oh [laughs]

Charles 19:24
We just don’t know. This is what I’m saying about not having enough… a lot of what we know about ulidiids is things that we think are maybe true based on what we have been able to demonstrate in other, often closely related, groups. So who could get inside Callopistromyia… this is again, when I think of Animorphs where in, like, the final book’s, like, in the post war “where are they now?” One thing that Cassie, who was always my favorite character, did… she wrote a book called Inside the Animal Mind, that was about how… having occupied, literally, animal minds, and so it was like a behavioral… it was like, this is… we, we actually have the experience of having occupied an animal body with all of its, like, animal instincts, etc.

And I think about that constantly, because that is, of course, what I would do, I would just, you know, get the DNA from every different insect that we’re interested in behaviourally, become them, and then probably end up stuck as a fly and die and not be able to publish. But if I didn’t think how I think what a valuable academic contribution that would be. So RIP Animorphs isn’t real… on the other hand, war is hell, so it’s good that, you know, positives and negatives to everything.

But yeah, so there are these different kinds of wing displays. But you are correct, in that we do know that different forms of wing displays are part of reproductive behaviors. So for instance, there’s one paper that is published on a species called Pseudodyscrasis scutellaris, and they have… I’ll include a link to this because one of the figures actually has the whole, like, flowchart of courtship behaviors. And part of it does include the male lifting up its wings in what they have described as “lofting” in the same kind of like 90 degree angle, so potentially, yes. And we also know that ulidiids, like their close relatives tephritids, engage in what is known as leks, so “l-e-k-s,” which is, quote, “a lek is an aggregation of male animals gathered to engage in competitive displays in courtship rituals known as lekking to entice visiting females, which are surveying prospective partners to mate.”

Tessa 21:42
I did not know there was a term for that.

Charles 21:44
Yeah. So it’s basically… a bunch of horny males get together, and they all display together. And they’re like, hey, check me out. And then hopefully females check them out, and then they get to reproduce.

Tessa 21:55
There are jokes one can make about frat boys based off this.

Charles 21:58
They could never… Because I mean, because part of the idea of a lek, of a lek is that you’re displaying, like, valuable characteristics.

Tessa 22:06
Oh, good point. Good point.

Charles 22:08
And then this is seen in, you know, a variety of species where they have these different behaviors involving their wings. But another thing that I wanted to get into in a little bit more detail is the idea of jumping spider mimicry. So are you familiar with salticids, do you know about jumping spiders?

Tessa 22:24
Yes, they’re the, you know, they don’t usually sppin in webs. Instead, they jump… they tend to look kind of cute.

Charles 22:30
They’re very cute, you can say it. And they tend to be fairly small, pretty furry and very, very cute because they have kind of tucked in legs and really big front facing eyes, which taps into that, like, huge eye cute complex that humans have. This is also, I’ve heard, why people like babies and anime characters, but I prefer spiders to both.

Jumping Spider mimicry is a really, really common phenomenon. In insects, there are models that are jumping spider mimics, very obviously you look at them and you’re like, oh, if I had like, the weak, relatively weak eyesight of an insect or a spider, I would be like, Oh, that looks like a salticid, that looks like a jumping spider to me. And there’s actually demonstrated jumping spider mimicry, in a tephritid specifically, of the species, Zonosemata vittigera, or [tries different pronunciation]. Listen, there’s no correct way to pronounce the species name because they’re fake words. Zonosemata vittigera is a tephritid that has very clear spider mimicry. So it’s interesting, because in this species, its wings… let me actually bring it up so that you can look at it.

Tessa 23:47
Oh yeah.

Charles 23:48
Mmhmm. And you can see on its wings, that it if you had, like… imagine that you are an insect, or a jumping spider, and you can’t see details that well, you can kind of see general shapes… that would look like a spider to you.

Tessa 24:02
Yeah, yeah, I see it.

Charles 24:03
Yeah, there was a paper published in 1987… so this species also has a wing waving behavior, where they hold their wings up, and they sort of wave them as if it were a spider kind of scuttling around.

Tessa 24:17
Hmm, yeah.

Charles 24:18
And so in the paper, what they did is, they took the wings off of the fly, and they did two things – they attached the wings to a different kind of fly, and they attached a different kind of fly’s wings to that tephritid, and they put them next to jumping spiders. And what they found is that the actual species – with those specific wings, moving the wings around – were able to sort of scare off the jumping spiders, where the jumping spiders would see them, and they would be like, Oh, it’s another Jumping Spider, and they would kind of back away. Right? And this was not the case for the flies that had those wings, but not the behavior, or the flies that had the behavior but not those wings.

Tessa 24:59
Not those wings, interesting.

Charles 25:00
Yeah. So the mimicry was both in the physical visual mimicry of looking like you have spider legs on your wings, and in the… specifically moving them in a way that you would look like how a spider might move around. And this is interesting, (a) by itself and also, (b) because there is one genus, at least, of ulidiids that have a comparable kind of patterning on their wing. And so if you look at these wings in a different way, but in kind of, I feel like you can kind of see, right, like, if you look at it, they kind of look like a set of legs…

Tessa 25:41
Yeah, yeah, I totally see it.

Charles 25:42
Yeah, there has not been that I can find any behavioral analysis of this fly at all. But when I was looking for examples of jumping spider mimicry, I did find another paper, talking about not moths, not flies, but a fulgorid planthopper. Basically, hoppers are, like, a group of hemiptera… you, you grew up on the East Coast, if you, like, walk through just, like, a field of grass, all of the stuff that kind of hops up around your feet as you walk through. Do you know what I’m talking about?

Tessa 26:14
Okay, yeah, yeah, Iknow exactly what you’re talking about.

Charles 26:16
Yeah, those are hoppers. So a fulgorid planthopper nymph that mimics jumping spiders. And in that paper, they described it as, quote, “the nymph has four smooth, polished dark areas on its meta thorax and hind wing pads that resemble the anterior eyes of jumping spiders,” meaning that on the sort of dorsal – the back part – of the plant hopper nymph, so before it develops wings, it has dark areas that look like the eyes of jumping spiders, because jumping spiders have these very distinct, big round eyes in the middle. If you will look at the pattern of eyes on a Jumping Spider, even totally decontextualized, if you’re familiar enough with them, you’ll be like, Oh, that’s a jumping spider.

And this is interesting to me because Xanthacrona both has these jumping spider mimicking looking wings, and it has these distinct dark spots on it scutellum. So this is actually one of the like diagnostic, i.e. telling different species apart, features is that it has, where on the scutellum, which is sort of this bumpy part sticking up from the thorax of flies, it has these black, sort of shiny spots. If you were to look at it from a certain perspective, holding its wings up with these bright spots, and you had bad enough eyesight that spider mimicry would work on you, it would look like a jumping spider. So that’s one aspect of wing stuff is… these courtship displays, otherwise probably courtship but generally ambiguous displays, and then also this specific example of mimicry.

And speaking of mimicry… imagine “everybody wants to be a cat.” But instead it’s everybody wants to be an ant. Because ant mimicry is very, very, very common, and Ulidiidae is no exception. There are at least two Nearctic species that have ant mimicry of like different kinds of ants. There is the species Myiomyrmica fenestrata, and then the species Myrmecothea myrmecoides, and you can tell… even if you didn’t know anything else about these flies at all, you would be able to look at their names and go, oh, ant mimics because they both have “myr” in there, right? Because that’s also like… myrmecology is the study of ants, myrmecologists study ants. Myr is… if you see “myrm” anywhere, you’re like, oh, ants, so just a hot tip to everybody in the audience.

And I tried to find more information about why ant mimicry happens so commonly, and I think the best, sort of common knowledge about it, like the common wisdom about why ants, why everybody wants to be an ant, is that ants are extremely populous, they’re all over the place, and because ants make formic acid – which is where they actually got their family name, Formicidae – they tend to not be very… like you don’t want to eat ants, right? And so I think ant mimicry is like, Don’t, just don’t… don’t. They’re both kind of spindly, and ant like, and I think has long legs, and that’s all, that’s all I have to say about ant mimicry, just a little bit of fun… [interstitial sound]

Going back to reproductive behaviors, like… this is what makes a lot of different groups interesting. And not just because I’m a freak but because it’s interesting, and it is very important to evolutionary biology because you can’t evolve if you don’t reproduce. Beyond wing stuff, there are a couple of really distinct morphological and behavioral characteristics that are demonstrated in ulidiids, among other kinds of flies. If I said “sperm expulsion” to you, what does that bring to mind?

Tessa 29:54
Is this where, like, you know, a female has mated with a male and then another male comes along and tries to remove the previous male’s sperm?

Charles 30:01
Well, in specific here… no. But in general, that does happen, yes, which actually gets into an interesting thing of… sort of how people often talk about, like, the reproductive arms race of evolution, where everybody is trying to control their own reproduction maximally, and that often leads to evolution of sort of oppositional sexual characteristics. So that is particularly… we see that in, like, beetles, where they have these very weird aedeagi, which we’ve talked about before, which are basically bug dicks, that are very spiky and can sometimes take out previous matinsgs’ sperm. I think this also happens in odonates, like dragonflies and damselflies… but sperm expulsion in Diptera as a behavior is present in three families that I know of: Piophilidae, Empididiae, and Ulidiidae, and in Ulidiidae, it is present primarily in one genus, and it is not males trying to dislodge other males’ leftover sperm, it is females exhibiting post copulatory mate choice, meaning that after they’ve mated, they expel the sperm themselves.

Tessa 31:16
Yeah, if they decide it’s not worth it, or it’s not what they want.

Charles 31:19
Yes, and then they eat it.

Tessa 31:20
Hey, free nutrients.

Charles 31:21
Well, this is interesting, because there have been a series of publications on this the first one from 2010, most recent one from 2021, looking at three species of Euxesta, which is one of the really large and diverse, taxonomically under-reckoned-with groups of ulidiids. So Euxesta bilimeki, Euxesta mazorca, and Euxesta eluta, and again, if those are not how you would pronounce them, I don’t care.

Tessa 31:48
Too bad

Charles 31:50
Too bad. Looking at this behavior in a vacuum, not knowing about it, there are kind of these two primary hypotheses for why this would happen. One is the nutritive value, because reproduction is exhausting. So yes, there is potentially… if you have just mated and you have sperm, and you are now going to have to fertilize and develop and lay eggs, you’re going to need nutrition.

But then also, again, the idea of post copulatory mate choice where, maybe you don’t have as much front-end control over which individuals you’re mating with, but you always have the failsafe of, I don’t actually want you to fertilize my eggs, so I’m going to just… I’m just going to expel it all out of my body.

The nutritive value one is actually relatively uncommon. We talked about, I think in the bug dicks episode… I think we touched on the idea of the spermatophylax in Orthoptera. Because a nuptial gift is not unusual, but bundling up a nuptial gift in sperm …is.

Tessa 32:58

Charles 32:58
So we did talk about that previously in Orthoptera, which are basically just… the hoppy guys, right? Katydids, grasshoppers, locusts, crickets… there is this empirical evidence for kind of both options where in, I think, Euxesta bilimeki or Euxesta eluta, they found evidence that a female was able to basically just get all of it out of there. Like if they expel it, they can basically reduce the likelihood of paternity of that individual down to zero. But they also found when they put them through like nutrition trials of, quote, “except for starved females who lived longer when allowed to consume a ejaculates, ejaculate consumption had no effect on fitness. Results suggest that females can bias sperm storage according to male mating effort, while the consumed ejaculate has some nutritional value, only evident when females were completely starved.” So it basically seems like the first string purpose of this is post copulatory mate choice, and then second string, if you are literally starving… tasty little snack to get you going.

Moving from the behavioral realm to more of the morphological one, Ulidiidae is one of a collection of families of flies that exhibits a trait called stalk eyes. Tessa, do you know about stalkeyed flies?

Tessa 34:22
I seem to recall hearing, or at least I’ve seen pictures of them. You know, their eyes are mounted on stalks and in some cases the stalks can become a ridiculous length because, I think, it’s like a form of, from an evolutionary point of view conspicuous, conspicuous consumption and has to do with mate choice. Basically, look at me I’m so fit and healthy and worthy of caring on your reproductive line that I can have these absurdly long, incredibly impractical stocks for my eyes and not get eaten.

Charles 34:51
I mean, basically, yeah. So stalk eyes are interesting because they are generally a sexually dimorphic trait, but there are monomorphic species of stalkeyed flies, i.e. both males and females have their eyes on stalks. The idea in these dimorphic species, ie males have one set of traits and females have another set of traits, is that it is a demonstration of genetic fitness to thus have better luck on the marriage market.

There is one genus in ulidiids that has this characteristic, it’s called Plagiocephalus. And they can get quite ridiculously long. And it’s also interesting because eyes are actually a really common location of sexual dimorphism in flies in general. So for instance, love bugs, which are known as love bugs because mating swarms can be a real nuisance… but they belong to the family Bibionidae… you can always tell if you’re looking at a male or a female, because of what their heads look like. So males tend to have much larger eyes in general, in sexually dimorphic groups in Diptera, than females.

I was like, well, this is interesting. And so I went looking in the literature to see what I could find on sort of the context around stock eyes. And there is actually a pretty robust library of articles that you can read, because the idea that we hammered home in evolution is that natural and sexual selection can be in conflict with each other, right? Where you have traits that make it harder for you to live, but easier for you to mate. The classic example being peacock tails, classic to the point of being banal, right?

Tessa 36:30

Charles 36:30
Where, if you got that big old peacock tail, it’s a real nuisance.

Tessa 36:36

Charles 36:36
You can’t fly as well, and it’s big, and it’s always there, and it’s dragging you down. But if you can flash them up, and be very impressive to females, it doesn’t matter if you die two seconds after you reproduce, you’ve reproduced, right. And so there is this conflict between living long enough to reproduce and to reproduce frequently, versus you know, these traits are not great to have.

But I was looking into the effect of sort of, it’s very inconvenient to have these big eyes. I mean, is it’s probably beneficial at a certain point… it’s been, I’ve seen it suggested that having this wider eye profile does give some benefit in, like, peripheral vision and overall vision, being able to see a wider range of stuff. And I think this is potentially borne out in Plagiocephalus, where the males have these absurdly long elongated eye stalks, but females still have more of a triangular than a round head shape, their eyes are set a little bit off from the center of their face. And so there is some potential initial fitness benefit of being able to see more around you, but at a certain point, it’s like…

And I was able to find a couple of articles talking about compensatory mechanisms in like flight to deal with, if you got these big eyes, your ability to navigate yourself in the air is modified. And so they actually found that there are these compensatory mechanisms both behaviorally, and in some sexually dimorphic species, the males had overall larger wings than females in those same species. And this difference in wing size was not present in like monomorphic stalk-eyed species. So like they were able to correlate larger wings in specifically males of species that have sexually dimorphic stalk-eyedness. So males that had large eyes also had slightly larger wings. So they lost some ability to fly with huge eyes, but then regained some of it again, with having larger wings. Evolution!

Tessa 38:48
That is wild.

Charles 38:49
I’ll include links to these articles that I found, because they are generally really interesting. [interstitial]

Ulidiids are quite a modest little group. Like again, they don’t have a lot of species and it’s also… a lot of what we can kind of potentially assume about them, we have to kind of project onto them from demonstrations and empirical research that we have on closely related groups or on groups that have similar characteristics because there just is not a lot of non-taxonomic work on ulidiids except in a small handful that demonstrate agricultural pest status. So most ulidiids, unlike tephritids… tephritids are pretty much all phytophagous ie they eat living plant tissue and this is why they are agricultural pests, because you don’t want insects to do that. But ulidiids are primarily saprophagous meaning that they eat stuff that is already dead or rotting. So they tend to be on, you know, rotting vegetation, rotting fruits and vegetables. There are some that oviposit underneath bark and their larvae are generally assumed to feed on beetle frass, ie beetle poop, rather than on the beetles themselves or on the wood itself. But there are some independently evolved groups of ulidiids that are primary pests on living plant tissue. And they are, there’s like a couple of species of Tritoxa, which are on onions, so Tritoxa flexa is the black onion fly. You’ll never guess what color it is and what plants it’s pestiferous on. [pause] It’s black and it’s onions

Tessa 40:31
Sounds… yeah.

Charles 40:32
Yeah, then there’s Tetanops myopaeformis, which is the sugar beet root maggot, which as a maggot is pestiferous on sugar beet roots. Entomologists have a lot of positive traits, but creative names are not among them.

Tessa 40:48
I mean, I have to admit there’s a certain amount of practicality in the naming structure though.

Charles 40:52
Well, exactly. And then there are also some Euxesta and a couple of Chaetopsis species that are primary pests on corn. And the females will oviposit like right along like inside the corn silk, and then the maggots will hatch out and they’ll lead the court. So there are four orders of insects that are unambiguously accepted as megadiverse. There is Hymenoptera, which is wasps, bees, ants and sawflies. There’s Coleoptera, which are the beetles. There is Lepidoptera, which is butterflies and moths. And then there’s Diptera, which is the true flies and all four of these have on the order of hundreds of 1000s of described species in hollow metabolise insects, there is a conversation of why are the megadiverse orders megadiverse right, why are they where they are in the insect tree of life? Why are there several hundred thousand beetles and only several thousand cockroaches. And one of the answers that has been given on why holometabolous groups have all of the megadiverse orders and in general are more speciose… part of it is the idea of niche partitioning / niche differentiation, where if you have a larval form that is very, very different from your adult form, you basically have non competition between different stages of life.

Tessa 42:13
Oh, yeah, yeah, not to bring up butterflies again, but this is like the suspected reason that, you know, caterpillars occupy such a different niche than butterflies.

Charles 42:21
Exactly. And this particularly gets into kisara and sheis offer of having these maggot maggots, where all they do is adults will lay their eggs in the soft substrates, maggots will hatch out of the eggs, and they have basically no physical traits, except what they need to be able to keep moving themselves around in the soft substrate and eat themselves to the point of pupation, then they often drop into the dirt, pupate, emerge as adults, and they have totally different behavior and totally different ecology.

Which I think is is a nice thing to end on, which is that most Diptera don’t have a true ovipositor. So most Diptera have lost a dedicated ovipositor. And what has happened in the tephritoids is that they don’t have quote unquote, a true ovipositor IE, a distinct specific apparatus for that, but their terminalia, ie the terminal segments of their abdomen, have developed into a long, hardened ovipositing tool that they can then use to, you know, stick inside of different substrates and oviposit, ie, place eggs there.

And so that’s an interesting shared trait among tephritoids. And again, going back to when I worked for a year on Anastrepha, I spent hundreds of hours of my life pulling the little aculeus, which is the very like tip thing, and looking at them… I had to use a minuten pin, which… a minuten pin will be familiar to any entomologist listeners, they are these teeny, teeny, teeny… so most entomological pins you can get in different sizes. There’s like zero to four, and you use different sizes of pins for different sizes of insects. So very large insects, like a carpenter bee, you would use like a, like a herdy boy, right, like a three, and then very, very small things you would go down to zero.

And then once you get a certain amount of smallness, you don’t even pin the insect specimen specifically, you point it, where you take a little triangle of acid free paper, and you glue it to the side of the insect thorax, and then you stick a pin through the point. But you can also do… what happens a lot in things that are bad for gluing, so a lot of like teeny teeny tiny little moths, because they have so many little hairs, it’s hard to glue them – they just come right off. So there are minuten pins.

So they’re these tiny, tiny, tiny, very thin little pins that you stick to a little block you put the larger pin through that block, you put the little pin into the thorax of tiny fragile things, I’m getting into very specific details so that you know exactly how small… so I have this tiny little minuten pin, and I would stick it inside of the ovipositor and I would pull out the little, like, aculeus that had these ridges along the bottom… and like the triangular shape that is used to like cut things open. Basically, ulceration is very common on ovipositing tools so that you can cut open something and then oviposit inside of it. And I spent hours, literally hundreds of hours of my life just very delicately pulling this tiny, tiny little apparatus out of the terminalia of… not particularly large flies, all of this in service of protecting agricultural crops. So thank… well, first of all, for your food, thank farmworkers who were grossly underpaid and mistreated. And then way down on the list after you thanked all of the farmworkers and advocated for, like, migrant worker rights… so after you’ve done that, then throw a very casual thank you to an entomologist.

So, Tessa, that was Ulidiidae.

Tessa 46:15

Charles 46:15
I hope you’ve enjoyed this trip.

Tessa 46:16
I did.

Charles 46:17
And I hope everybody in the audience will take a moment in their lives to look closely at a plant, and hopefully they’ll see a little fly there. And maybe it’s moving around, just vibing and just living its life, and I hope that they’ll take a moment to appreciate that flies are massively diverse, massively interesting, beautiful in their own unique way, and important ecologically to the world as pollinators, as food, as predators, as parasites, as… [fades out, interstitial]

If you want to find me in general online, I am on Twitter @cockroacharles, and Tessa?.

Tessa 46:59
I am on Twitter @spacermase.

Charles 47:03
The show is on twitter @ASABpod or at our website where we post show notes and transcripts for episode, asabpodcast.com.

Tessa 47:10
And until next time, keep on science-ing.

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