Fly with ant-mimic wings

November 5, 2013 • 12:17 pm

Several readers have called my attention to yet another amazing case of mimicry, this time in a tephritid fly (the “true” fruit flies). Most people became alerted to this by a semi-viral tw**t by Ziya Tong, which notes that “Goniurellia tridens is a 3-in-1 insect,” and that the photo below was taken by Peter Roosenschoon in Dubai. Roosenschoon is a conservation officer at the Dubai Desert Conservation Reserve.

Those aren’t ants bedecking the fly’s wings; they’re the normal wing markings of this species. But why would a fly have antlike markings on its wing? [UPDATE: Note comments at bottom where an ant expert and two others (including Matthew) think that these are spiderlike markings.  I’m coming around to that point of view.]

The issue is discussed in a New York Times‘s “Dot Earth” column by Andrew Revkin, which refers back to the original article in the original article by Anna Zacharias in The National, a United Arab Emirates newspaper. Zacharias describes it:

The image on the wing is absolutely perfect,” says Dr Brigitte Howarth, the fly specialist at Zayed University who first discovered G tridens in the UAE. [JAC: the species has been known since 1910, and is found in the Near and Middle East, Asia, and Asia.]

. . .In the UAE alone, 27 picture wing species are known. Some have wings bearing simple shapes but others, like G tridens, are far more complex.

Dr Howarth first saw G tridens on an oleander shrub in northern Oman. “I was looking at the stem of the leaves and I noticed that there were some insects crawling around. When I sort of honed in I started to notice what I thought was a couple of ants moving around.”

At first she suspected an infestation on the fly’s wings. “But it was so symmetrical that I thought, ‘oh this is not possible’. When I got it under the microscope I realised that these were insects painted onto the wings.”

In contrast to its wings and brilliant green eyes, the fly’s body is a dull greenish grey – “almost cryptically coloured,” says Dr Howarth – that blends into the leaves where it is found

Here’s a photo (uncredited) of a pinned specimen from The National:

Screen shot 2013-11-05 at 4.54.26 AM

But why the ant markings? Howarth, interviewed by Zacharias, explains:

When threatened, the fly flashes its wings to give the appearance of ants walking back and forth. The predator gets confused and the fly zips off.

That doesn’t make a lot of sense to me.  Why doesn’t the fly just “zip off” by flying away when it sees a predator? Confusing a predator by waving your wings just wastes time.  Now some tephritids have spider-like markings on them, and that makes more sense.  Apparently the predator is a jumping spider, and when it sneaks up on a fly, it sees the spider markings, mistakes them for another spider of its species, and displays to it. That display gives away the spider’s presence, allowing the fly to get away.  But I can’t see this happening with ants.

Howarth also suggests a sexual function:

This defence mechanism may also make the fly attractive to potential mates – something that is less of a concern for the average housefly.

“A lot of flies, if a male sees a female that is suitable it just flies up and tries to latch on,” said Dr Howarth. But G tridens has an altogether more amorous courtship, showing off its wings in a colourful dance. And Dr Howarth believes it is no exception.

“If you look at the behaviour, it tells you a lot about the functionality,” said Dr Howarth. “Not everybody gets to mate. The ones that do have something about them that make them more attractive.

“Is it the same in other invertebrates, who knows? It’s very possible that those are in fact for courtship behaviour.”

That makes even less sense.  Yes, marks on the wings can help courtship, but why would ant-shaped markings on the wings be necessary for that? It’s not like females are attracted to ant shapes because the flies eat ants, because they don’t. No, there’s something here about the resemblance to the ants that facilitates the fly’s survival or reproduction.  Howarth’s final statement doesn’t make a lot of sense to me, either:

This elaborate behaviour may be a response to the fly’s restrictive environment. “Something that can survive anywhere doesn’t need to have as many protection factors,” said Dr Howarth.

The more realistic the picture on the wing, the better its chance of survival and reproduction.

The truth is that we don’t really know why this fly has antlike markings, but we can predict that studying how the fly uses its wings, and knowing more about its ecology, will suggest some testable hypotheses. I’m too harried to think about alternatives now, but I bet some readers, particularly our entomologists and field biologists, can suggest an evolutionary explanation for ant markings.

Finally, here’s a flickr picture by Drew Gardner (I cropped it a bit), who notes, “Another pictured wing fly. This is a small fly about 3 mm long which came to the mercury vapour light. Each wing has an almost perfect picture of an insect, complete with head, thorax and abdomen and six legs.”

Screen shot 2013-11-05 at 5.01.24 AM

h/t: Diana MacPherson, Matthew Cobb, and several others I’ve forgotten (sorry!)


EDIT from Matthew Cobb: Not everyone agrees with the ‘ant’ diagnosis. Starting with ant supremo Alex Wild (a.k.a. @Myrmecos). The following discussion took place on Tw*tter.

75 thoughts on “Fly with ant-mimic wings

    1. Ben,

      I think they are likely jumping spider mimics. Found in Tephritid flies (although wings+spots are used to mimic spider aggression). We think we found them in another family of Diptera as well. Remind me to show you the video.

    2. Is it possible that those markings were supposed to scare potential treat? The figures have their heads pointed away from fly – as if they were jumping away (probably it looks this way when fly flaps its wings) – otherwise why the markings were not having their head pointed towards fly?

  1. Is there something protective about the kinds of ants that these flies hang around? Do those kinds of ants taste really bad?

  2. My questions is–do the other arthropods in question really see these markings the same way we do? In other words, the markings look like an ant or a spider to us, but would they look that way to a predator or mate?

    1. Leslie:

      I just finished your book, “Spider Silk”. Fantastic! Let me recommend it here for everyone, arachnophobic or philic, as there is some truly amazing biology in the book, as well as a straightforward presentation of the evolutionary context. Great stuff!

      1. It’s on my list (and literally on my to read shelf on my book shelf not just on my Goodreads list). I’m looking forward to it!

  3. It may be that the fly moves it’s wings in the mimic behavior habitually, rather than as a response to spotting a predator. That seems more suitable to combating an ambush predator, allowing anything that delays the predator or causes it to strike less accurately to be advantageous.
    As far as mating, it is not hard to imagine that any beneficial trait could give rise to a corresponding sexual selection behavior, and then co-evolve with it. That kind of parallel process is one of the hallmarks of evolved systems, and it could certainly allow for much more rapid and accurate development in cases of mimicry traits.

    1. Now that you mention it, it doesn’t look like anything specific, but it sure screams “terestrial arthropod”. Hell, maybe it’s difficult to pin down as part of its function. “Are those tasty flies, yucky ants, or dangerous spiders? Oops, there they go.”

  4. I can remember from my youth lots of pictures of ants attacking insects and I recall they first climb onto the wings, presumably to stop it flying away.

    Maybe ants wont climb onto wings that already have ants on them and so the fly has an extra chance to escape.

  5. Lucky fly! I wish I had spider wings to scare people away. Come to think of it, probably the scariest thing would be wings depicting cellulite! That shit’s scary! 😀

    I think this is so cool though – how the image looks painted on!

  6. That fly species has those amazing markings on their wings because our blessed Lord and Savior wants them to.

    See how easy this stuff is if you just let a little Jeezuus!!! into your heart.

  7. I vote ant. Spiders do not wander in pairs; ants do. Predators are not dumb.
    The images are about 1.5 mm long. Too small for a spider; just right for a Crematogaster ant — nasty little buggers that swarm on plants in warmer parts of the world. Nothing much eats them, and that’s probably why they swarm.
    Do the figures have 8 legs, or 6 legs and 2 antennae? Dunno.
    As usual, we need to know some ecology.

    1. Maybe it appeals to the horror of the unexpected doubling up of spiders!! I did once see two spiders traveling together across the lawn. Weird since they often eat each other.

  8. I am wondering about the relationship between flies that use wing patterns to mimic spiders or ants, and flies that use wing patterns in territorial and mating displays. In many cases the patterns are rather similar, as anyone can see by looking up pictures of Tephritid or Drosophilid flies.
    So one scenario could begin with selection for wing patterns used in mating displays. On some occasions some flies also benefit since the wing patterns and wing waving behaviors used already happen to also resemble a spider or ant. This then leads to selection to improve on that, while still using the patterns for their original purpose.

  9. In the 70’s I worked for Guy Bush at the University of Texas for a couple of years. A lot of his work on sympatric speciation involved the Tephritid fruit fly Rhagoletis pomonella, the Apple Maggot.

    Their wing markings also bear great resemblance to spiders, to the point that every time I picked up one of the clear plastic boxes we were raising them in, I flinched a little bit (being sadly a bit of an arachnophobe, though I do also love spiders).

  10. Why doesn’t the fly just “zip off” by flying away when it sees a predator?

    Some predator set traps which might temporarily prevent a fly from zipping off. Some can catch a fly while its in flight. In both cases, a temporary distraction would have adaptive value.

    I’m not saying that anti-predation is the reason, but I wouldn’t be so quick to dismiss it. I can think of several situations where making a predator hesitate for several moments or move off is better than simply trying to get away.

  11. Maybe the bug designs resemble a predatory fly that leaves its egg(s) on/in this kind of fly, and displaying that it has already been ‘parasitized’ fools other circling predators that they’ve been beaten to the prey.

  12. I was thinking that they’re not necessarily scary, but would lead a predator to attack the heads on the wingtips… which is a lot safer for the fly.
    You would need to see who/what responds to those patterns and how, to know whether they are sexy or scary or just confusing.

  13. The markings do look like Salticid spiders- even a little like ant-mimicking salticid spiders, which would probably be scarier to ants than normal spiders, while being spider-like enough to warn off other potential predators such as robber flies. It is interesting that the markings are facing away from the body as well, almost like sentinels. I think looking at a video of these flies and the way they position themselves on alighting may also be helpful in determining their function. If I were a predator of flies, I would certainly think twice about approaching this one.

    1. Interesting, it seems some super sleuths have uncovered evidence that it may indeed be a hoax and this article nicely compares wing patterns of other flies and explains how the patterns that mimic spiders/ants do so when the wings are back, not when in the resting position of the photo.

      Someone needs to find out where the photo originated.

      1. I just googled the original photographer, and there are at least four pics of the same fly on different backgrounds, so if it’s a hoax, it’s a pretty elaborate one. If the fly is like similar flies I have seen they do swivel their wings back and forth at rest. I think it’s legit, but if someone can convince me otherwise, I’ll accept it.

  14. A few comments (1) There is apparently a lot of variation in the patterntrying to find more detail based on these small picture samples than is warranted. But the pattern there, so what would a pattern on the wings be useful for? It could simply confuse a predator because it is hard to interpret. Look how many different interpretations we are making. That may be all it is; that small bit of confusion provides an advantage. If the pattern looks like other bugs, perhaps the predator has tries to attach those. If they look like eyes, then this could confuse a predator. It may cause a predator to hesitate or it may cause them to strike at the back of the fly rather than the head, which may result in fewer successful predations. It doesn’t have to be a dramatic effect; even a small effect over such a large population will matter. (2) What are the wavelengths of light that the insect’s predators see best? We should really be looking that these markings in those wavelengths so know what the predator sees. (3) If these markings are ‘intended’ to look like another insect, then to me they look like they are facing in the opposite direction from the actual fly; that may be important. I am completely making this up, but perhaps a predator of flies has a bias in it’s strike based on how the fly may take-off to avoid the strike. Like how you can more easily catch a house fly by trying to capture it from the front, rather than the back, so it may fly into your hand. If that is true, then this could offer a larger advantage than just a confusing marking.

  15. I think this is just an instance of humans “seeing” an “intended” pattern where in fact none exists. Moreover if you’re told it’s an ant you’re going to believe it’s an ant.

    Looking in close detail at the Flickr image posted here doesn’t look “perfect” at all – just a variant of normal wing patterning.

    It seems to me it’s just a slightly different spin on the well-known phenomenon of people reporting the Virgin Mary on a piece of burnt toast.

    We’re all programmed to recognise patterns. When my wife went on a two hour therapy session to deal with her arachnophobia (which worked well!) while I was waiting for her, I got talking to another woman who was waiting for her treatment. She described her last “spider incident”, where she woke up in the middle of the night and “saw” one on the wall. Petrified, she rang her Dad and got him to come round at 3am to move it. When he switched on the light, it was found that it was just a mark on the wall.

      1. I think you’re wrong. Mimicry is a real phenomenon, and has clearly been fine-tuned by natural selection in this and many other cases. There is no other explanation for the information content of the complex wing patterns.

        1. If toast reproduced conventionally the virgin mary toast would not have been eaten and may have continued to breed, and there is a chance that an inedible line of toast would have sprung up, in a similar manner to the famous Samurai crabs of Japan. So even if pareidolia is indeed the case, it doesn’t in fact lessen the case for the evolotion of salticid-like markings on the wings of flies.

  16. Looks like a spider, a whitetip spider to be specific but without the white-tip, the elongated thorax and abdomen. Now imagine you want to eat this little fly. Would you if you saw two whitetip spiders (ferocious predators on other spider) there…..hmmm nope = increased fitness = fixed….. Now a female of the species says they’re aren’t real but they look pretty, would you like to sleep with me? Very easy to imagine. v.v.v. cool

  17. Initially I thought this might be a hoax, but I’ve come around. A Google image search on Goniurellia brings up a scientific article by Merz 2002 published in the journal Revue Suisse De Zoologie. Figure 11 shows wing markings of another species in the genus that look very similar to those in the photos being circulated.

  18. There are lots of possibilities with this trait. What the shapes are ‘supposed’ to be is a bit of a silly question. No mimicry is perfect, so all these shapes have to resemble is something that the flys main predators don’t find palatable. It could be a spider or an ant or a louse; so long as it confuses the predator enough to allow for the fly’s escape. As someone mentioned previously, it may have evolved to resemble an amalgam of traits that simply scream ‘unpalatable terrestrial arthropod.’ The fly’s cryptic camo attests to the fact that the predator isn’t supposed to even see the fly’s body-proper.

  19. Given that other individuals of this species are observed with non-mimicry markings (i.e., more random in form), this is perhaps just another random set of markings, a point along the curve of variations from unspecific to apparently very specific. The “mimicry” may be just a subjective impression on the part of the observer. I did not read anything in the article referring to a close match to an actual insect or spider species in this fly’s habitat, so if any “mimicry” were plausible, it would need a co-existing model on which to base its resemblance. If this were truly adaptive and gave the bearer an advantage over other individuals of its species, you would expect this pattern to become more or less universal in the fly population in question. But it’s not, apparently, so “Virgin Mary in the toast” seems the most plausible explanation.

    1. My thoughts exactly. A lot of “mimicry” cases have no models and serve no obvious function. I would say these markings are not necessarily functional and therefore not necessarily refined gradually by selection pressures. If the markings on this species tend to vary, than the probability of one or a few markings looking like other bugs strictly by chance may be fairly high. Do we know how true this form reproduces?
      I’ve written about Vladimir Nabokov’s views on the subject of non-utilitarin so-called mimicry. He appreciated the pure chance behind some amazing forms. Some people who can’t accept “pure chance,” insist it had to be god or gradual natural selection that created it, with about equal enthusiasm and irrationality.

  20. Most definitely a spider. On those transparent wings, elevated and angled, if you take both sides together it becomes three dimensional. It reminds me of a hologram. You have to remember that it was developed to be seen from a spider’s eye view. The “dummy” would have two “eyes” and legs out to each side, out-facing a pedator sneaking up from behind which is the fly’s weakest point – the fly not being able to see behind or to take off backwards. A spider would probably not instantly attack one of its own kind, giving the fly time to escape.

  21. Really need to know what it’s main Predator is. I am interested in the confusion effect and wondered if by waving about its wings when detected it gave the impression of a small moving aggregation thus reducing strike efficiency. Alternatively it might give the predator three choices instead of one so improving it’s own chances. No doubt some crappy ‘isn’t evolution amazing’ Science paper for someone with a bit of time on their hands.

  22. I believe this is evidence that flies can form and join gangs. I believe the ant-like markings are actually gang colors. In fact, I have witnessed Drosophila in the lab displaying gang signs with their appendages. It’s really quite remarkable.

  23. In all of the pictures shown, the wingspots resemble two smaller flies, pointing in a different direction than the fly itself . this could help it to escape predators if they try to predict what direction the fly will attempt to take off. in if it is attacked.

  24. One may well ask whether the wing markings are adapted to function as lures or threats. If the spider (or ant) images function as threats, they may deter close approach by predators, potentially including predators that the fly has not perceived yet.
    As the fruit fly is presumably not itself a predator, the ‘lure’ possibility may seem strange, but analogous mechanisms are known in vertebrates: for example, the waving of tails or forelimbs by lizards that cause a stalking predator to approach, giving away its position to the motion-sensitive vision of the lizard while the predator’s own vision is compromised, allowing sudden escape.
    Whether a signal is a threat or a lure (on a particular occasion) is an empirical question, i.e. whether it induces approach or repulsion. The intermediate cases, turning or freezing without moving away or towards the signaller, may be ambiguous but are usually best considered to fall into the ‘threat’ category. The same signal may have different effects at different times on the same recipient, for example acting as a lure at greater distance and threat at close range. Snakes do some cool stuff with tail-waving, including the caudal luring well known in many species, and also (in some examples I described) threat displays used in flush-pursuit, getting hidden prey moving where it can be chased down.

  25. Does it matter what the species is on the wing? For crying out loud, it is marvelous that such an accurate picture of whatever species has become part of this insects wing! Life is mind blowing….accept it! admire it!

  26. to me i’m going to try and be unique and go with the markings mimicing phorid flies, which are nasty horrid little flies that the smartest ants and spiders both best avoid… even if it means missing a meal.

  27. The wing markings, remarkable as they appear to our eyes, don’t need to be specific and perfect mimics of anything. All that they need to be, is effective at confusing a predator long enough for the fly to effect a getaway.

    Of course, whilst this paper and its findings need to be taken into account (the authors document therein that they performed experiments to determine if the Salticid mimicry hypothesis was sound), ideally we need to wait until similar empirical work is performed on this species, before reaching for any unwarranted conclusions. I’m sure those readers that are part of the Tephritid research community will find this concordant with their own views.

    At bottom, all that a prey organism needs to do, in order to live to fight (and breed) another day, is find some means of supplying ambiguous signals to its predators, in a manner that results in those predators coming to a halt in confusion, instead of launching an attack. Ultimately, any mechanism that conveys a message to the effect “stop for a moment before treating me as lunch” will confer an advantage upon the organism possessing it, so that a predator will look for something that more obviously says “Hello, I’m lunch”.

    Of course, if said mechanism also confers an advantage when looking for mates, because the potential mate regards the signal as an invitation to breed, the organism enjoys a double win. I’m aware of several flies that use wing markings as a courtship signal (e.g., Poecilobothrus nobilitatus, Family Dolichopodidae), so it wouldn’t be too surprising to see a courtship signalling mechanism exapted for predator confusion.

  28. Meanwhile, from a different insect clade, we have this paper, in which Metalmark Moths of the Genus Brenthia were demonstrated, in controlled trials, to be Salticid mimnics.

  29. For some reason, the link to the paper didn’t work in my previous post. Try this link instead …

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