The amazing flies of the genus Richardia: sexual selection taken to extremes

January 28, 2017 • 7:30 am

I have a decent backlog of readers’ wildlife photos, but not enough to make me comfortable, so be sure to keep sending in your good pictures.

Today we’re taking a hiatus and featuring the amazing photographs of photographer and entomologist Gil Wizen, taken from his eponymous website (with permission; note that he also has a Twitter page and a Facebook page). I especially like these photos because they show the effect sexual selection can have on flies: in this case flies in the genus Richardia (the post from which I took these photos is “Photographing Richardia: a long way to victory“).

Gil’s photos were taken in Ecuador, and feature some really cool flies. (Note that these are copyrighted, and you must ask permission for both commerical or noncommerical reproduction.) Here, for instance, is an “antlered fly”, with Gil’s description (indented):

Males have antler-like projections from their eyes, which are used for pushing an opponent during a combat over territory or a mate. The female Richardia lacks those projections, but is characterized by a telescopic ovipositor at the tip of her abdomen, used for injecting eggs into fruits and other plant tissue.

The site also has an awesome close-up of the antlered head itself, so go over and see that. Here are the males: dorsal and frontal views. Note that the “antlers” are projections of the head itself, and are not antennae or aristae, which stick out straight in front in the first photo:



Richardia also includes ‘hammerheaded’ flies, in which the males (but not females) have their heads elongated laterally, resembling (but not related to) the “stalk-eyed flies” (diopsids).  The fact that only males have wide heads is a clue that sexual selection is going on, and indeed it is: in the form of male-male competition. As Gil notes:

The hammerhead Richardia can sometimes be seen on the underside of broad leaves such as those of banana and heliconia plants. Males engage in head-pushing tournaments while a single female usually stands by watching and waiting for the winner to approach. He will then display a short dance, running in circles and waving his decorated wings, before mating with her.

Clearly males with bigger heads have an advantage here; that’s what’s driven both the elongated heads and the sexual dimorphism. Here’s a male:


And a female of the same species, having a “normal” head:


Just to show the lengths to which sexual selection can go, below is a male from a different fly genus. Yes, those are the eyes on the tip of its head, and surely this design is not only maladaptive for fly vision, but also for flight. (If it were visually and aerodynamically good, the females would have it too.) Gil’s caption:

Male hammerhead fly (Plagiocephalus latifrons), dorsal view. One of the most amazing fly species out there in my opinion!

The behavior of this fly isn’t described, but I would bet $100 that the males engage in head-butting contests or “my head is bigger than yours” comparisons, with bigger-headed males generally winning. Of course, selection will only proceed to the point where the sexual advantage of having an even longer head is counterbalanced by natural selection against that lengthening, probably based on metabolic, visual, or aerodynamic constraints.

Look at that head!!:


Gil wondered, as did I, how these huge heads could possibly fit into a pupal case. I guessed, based on the fact that flies also expand their wings after they hatch, that these males can also expand their heads after “eclosion” (hatching from the pupal case). That in fact is what happens. In the amazing BBC video below, also posted by Gil (narrator sounds like David Attenborough), you see a stalk-eyed fly right after hatching. It gulps air bubbles and forces them into its head to expand the eyestalks!

Thanks to Gil for permission to use the photos and Matthew Cobb for calling my attention to Gil’s post.

Snarky aside: as one reader below noted, some misguided souls might suggest that this sexual dimorphism isn’t the result of evolution, but is simply a social construct: males are raised to have long eyes! Well, we know that can’t be true (how do we know that?). At any rate, male-male competition is also a likely a behavior that, imposing sexual selection, led to sexual dimorphism in body size in our own species, with males being larger and having more muscle mass than females.  Imagine what human males would look like if they had to head-butt to win a mate!

36 thoughts on “The amazing flies of the genus Richardia: sexual selection taken to extremes

  1. What I just saw in that video is one of the craziest things I’ve ever seen. What will natural selection think up next? Amazing.

    1. . . . sexual selection thinks up. Natural selection makes things that are ecologically useful. The two forms of selection work the same way as far as the selection of genes is concerned, but have very different functional consequences for the whole organism. The photos are very nice.

    1. I don’t know what the gods will think up next, but they’re puffing the weed, dropping the acid, and sucking a few exotic ‘shrooms already, so it’s going to be weird.
      If my glass-blowing were better (a LOT better), I’d make a hookah for mixing those drugs, and call it something like a Boringly Optimised Neohallucinogen Generator.

      1. Many moons ago I grew pot in the family back woods. I noticed the plants seemed to attracted an unusually attractive little sapsucker bug. They were decorated in luminous exotic patches of color like a potheads wall posters. I imagined they were enjoying a high while sucking hemp leaves and wanted to express their pleasure by showing iridescence.

  2. Great article.
    Just when I think I almost I have an understanding of a concept, I learn something new that pokes a hole in it. I’ve understood sexual selection as a way for one sex to select the “most fit” of the opposite sex for passing down her/his genes. This makes sense to me when I think about bucks or rams horn butting each other in front of females (see, I can produce offspring that will be able to fight off predators and survive). but, the elongated heads of these flies seem to be only deleterious to short term survival and serve no other purpose besides attracting females. The first thing that came to my mind was, “Why would the females be genetically disposed to this maladaptive to survival trait?” My two guesses are that either they show the female that, “Hey, look how burdened I can be with this head and still survive to maturity,” or maybe in an ancestor of the flies a slightly elongated head was a survival advantage and selection hasn’t had the time and/or environment to filter it out. I don’t know if that question has been answered yet (or even if it’s worth asking). But, it did get me thinking about it.

  3. This is bizarre. This is just one experiment where natural resources were abundant enough that these flies could do whatever they heck they wanted to do and still reproduce.

  4. Beautiful photos! Gil, if you are reading this and are still here in Ecuador, if you are looking for more places to work I invite you to come to our scientific station at 1600m in the cloud forest near Banos on the east slope of the Andes. The insects of this area are very poorly known.
    Google: EcoMinga Zunac

    1. Thank you, Lou! That is very kind of you. I am no longer in Ecuador but I visit very frequently (I try at least once a year). I would love to visit your reserve at some point, Banos area is beautiful and very interesting. Gil

      1. Great, we’d love to have you. We can get you into very remote habitats and help you with your logistics. Let me know a fair bit in advance. We recently hosted another regular WEIT comn

          1. Sounds good, thank you. It might take some time until I visit Ecuador again (maybe next October?). But I will definitely get in touch.

          2. Your photos are truly beautiful.

            An observation: I find flies, and most insects, to be gross and distasteful. But that is primarily because they are ugly. I associate drab colours, loud buzzing noises and creepy crawly appendages with danger/eww/gross feelings.

            However, an attractive, brightly coloured fly does not fill me with dread. I would be delighted if such a gorgeous creature were to buzz around my head.

  5. Interesting, I didn’t know about the sexual dimorphism in the stalk-eyed flies. I’d seen images of them before and wondered if it was some sort of adaptation to improve stereoscopic vision. But if only the males exhibit the trait, that wouldn’t be the case.

    1. Well of course it could. Males are *superior*.

      They also have a head full of air. Where do they keep their brains? (Do flies even have brains?)


  6. That’s amazing. I’m fairly sure I saw the original BBC documentary which aired this.

    I find it incredible that a would have preferences towards a mate.

  7. Fantastic photographs, nice examples of creatures new to me, thanks. Sexual selection, since learning of it’s ways to manipulate and create it has had my attention ever since.

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