Readers’ wildlife photos (spider mimics frog!)

We have only two photos today, both from Lou Jost, who’s been busy in the rain forests of Ecuador. But they’re great pictures, and one apparently shows a form of mimicry new to me: an insect mimicking a frog. Lou sent this yesterday:

In honor of your mimicry post today, here are two more mimics for your delectation, found this month during a visit by a group of Stanford University students. The first is a crab spider that imitates a frog! It was found by students Dylan Moore and Natalia Espinoza in EcoMimga’s Rio Zunac Reserve.

The EcoMinga page adds this:

 At first they [Moore and Espinoza] thought it was a frog. It holds its forelegs in a position reminiscent of the hind legs of a frog, and its abdomen mimics a frog head, complete with eyes. I imagine that small birds or insects that would catch a spider might not want to waste energy or risk their lives trying to catch a frog.This spider seems to be related to the famous “bird poop spiders” but I don’t really know. If an arachnologist reads this, perhaps he or she could add some information about this?

The next day,when we went to EcoMinga’s Rio Anzu Reserve, I spotted this leaf-mimic katydid only because it moved its two antennae together to act more like an inanimate leaf. It was confident in its disguise and did not move when disturbed.

You do see it, right?

The frog mimic a frog raised two questions, which I sent to Lou. Is this the first described case of a spider mimicking a frog? And what could be a selective advantage to the spider of this kind of mimicry?  Lou responded:

Jerry, I hadn’t ever heard of a frog-mimic spider like this, but the internet does reveal one other alleged example here [JAC: here’s the photo at the link]:

But I think that one might be imitating a snake head.

As to why a spider might mimic a frog, I don’t really know. Maybe insects that would eat spiders might be afraid of frogs? Or maybe birds that would eat spiders are not going to bother to chase a frog, which is more agile and which might be toxic?

It’s unlikely that the imitation is to help the spider sneak up on prey, as it seems that most prey that would be eaten by a spider would also be eaten by a frog. Also, the spider’s color is not an “aposematic” warning color, which most toxic frogs have, like this one:

Oophaga pumilio, the “strawberry poison dart frog”. It’s extremely variable in color and pattern; this one is the “blue jeans” morph.

That, I think, rules out the toxicity hypothesis, though not the agility hypothesis.

18 Comments

  1. Posted July 27, 2017 at 7:53 am | Permalink

    Very nice photos Lou. You must be using a proper macro lens …?

    • Posted July 27, 2017 at 8:32 am | Permalink

      No, when I am with students I must travel light and pay attention to them, not to my photography. In that situation I just carry my trusty Lumix FZ300 “bridge camera”. To get these close-ups I add a Raynox close-up lens that just clips onto the camera’s non-interchangeable lens.

      I did take the spider back to my house and made proper photos, a stack of 150 images combined into one using the Olympus 60mm macro lens. The lighting angle is not as nice as in the photo Jerry included, but the resolution is better. You can see that photo on the EcoMinga website:
      https://ecomingafoundation.wordpress.com/category/reserves/rio-zunac-reserve/

      • rickflick
        Posted July 27, 2017 at 10:09 am | Permalink

        “the resolution is better.”
        Indeed I clicked through to the full resolution and found plenty of detail. Amazing critter!

        • Posted July 27, 2017 at 12:12 pm | Permalink

          Even that was only a small fraction of the full resolution of that photo. I reduced it to upload it. With that Olympus camera I can make 80 megapixel images!

      • Posted July 27, 2017 at 10:46 am | Permalink

        Thanks!

  2. GBJames
    Posted July 27, 2017 at 7:55 am | Permalink

    This is sooooo cool!

  3. dargndorp
    Posted July 27, 2017 at 8:05 am | Permalink

    Very cool, but aren’t spiders classed as arachnids rather than insects (regarding the intro paragraph)?

  4. Wonderer
    Posted July 27, 2017 at 9:38 am | Permalink

    For frog mimicking spider…

    How about an ‘anticipated retreat direction’ hypothesis.

    It seems that predators might have less success at catching these spiders if the spiders tend to move to escape an attack in the direction opposite to the predator’s expectation.

    • Posted July 27, 2017 at 9:57 am | Permalink

      That’s quite a good hypothesis. It’s why many butterflies have fake antennae and eyespots on their hindwings.

  5. darrelle
    Posted July 27, 2017 at 9:40 am | Permalink

    I agree that the way the spider holds it front legs does seem to mimic a frog’s rear legs pretty well, but I’m not sold on the abdomen of the spider mimicking the head of a frog.

    The shape of the spider’s abdomen is odd compared to that of a typical spider and the shape of a typical spider abdomen seems like it would be better for mimicking a frog’s head than this spider’s. The odd shape of this spider’s abdomen makes me think that it was selected for something other than mimicking a frog’s head. Maybe that is indeed the case and we are seeing this spider at an early stage of evolving to mimic a frog?

    Or maybe the strange shape is the result of near equal selection pressures for mimicking a frog’s head and something else and the abdomen as it is just happens to be good enough to fool whatever critter(s) it is “intended” to while also suiting its other “purpose”?

    • Posted July 27, 2017 at 10:01 am | Permalink

      Yes, this does seem like a work in progress, and there may be several kinds of selection pressure going on at once. But I disagree that a normal, more or less spherical spider abdomen looks more like a frog head than this flattened, snouted, eye-socketed abdomen. Though you can’t see it very well in this picture, the “snout” is elongated and upturned much like a frog’s. All who saw it in life thought t was a frog at first.

      • darrelle
        Posted July 27, 2017 at 10:48 am | Permalink

        I wish I could have seen it in real life!

        And I forget to say, very cool critters and most excellent pictures.

  6. Posted July 27, 2017 at 11:37 am | Permalink

    Excellent finds, Lou! As for the katydid, it seems ‘wet’. Is that b/c it was wet, or was it shiny to mimic wetness?

  7. W.Benson
    Posted July 27, 2017 at 3:37 pm | Permalink

    Lou (& Jerry too), you are going to have to do better than that to convince sceptic-me that the spider even potentially mimics a frog. It does, I admit, have an abdomen that looks like the head of some nondescript frog, but it also resembles, more parsimoniously I think, a non-descript dried flower bud, seed capsule, or some such trash that fell and adhered to a leaf.
    My questions are:
    How big is the spider? Is it in the frog size-range?
    Are there frogs in the forest that are actually as small as the spider, look like it, rest in the open where they can be seen during the day, and are common enough to serve as models?
    Are there things that feed on spiders, and are repulsed by the small model frog, that would make resembling a frog advantageous for a spider? Wasps and birds do prey on spiders and would not be interested in frogs, but they would be equally uninterested in dried plant debris in general. Natural history work is needed.
    My personal opinion is that there are so many good, convincing examples of mimicry, why go out on a limb with stuff that can be used to portray hard-core adaptationists (like myself) as purveyors of just-so-stories. That said, the appearance of the spider is most intriguing.

    • Posted July 27, 2017 at 6:03 pm | Permalink

      Skepticism is welcome, and maybe I’m wrong.
      But it does not look like a random bit of trash;there are spiders that mimic such trash, and they do a good job of it. This on the other hand perches just like a frog, with the “nose” of the fake head raised well above the leaf, and the legs held where frogs would hold them. Everyone who saw it alive in situ thought it was a frog at first glance.

      Yes, there are frogs of the right size here, though both the spider and diurnally-visible frogs are rare.

      It is not required that the thing feeding on spiders would be repulsed by a frog. See the hypothesis in Comment 4 by Wonderer. The effect mentioned by Wonderer is a very powerful selective force in the tropics and would be driven by omnivorous birds, whose vision is good and who would certainly have experienced many frogs in this forest.

  8. Mark R.
    Posted July 27, 2017 at 6:45 pm | Permalink

    It looks like a frog to me. I’m especially convinced by the back “jumping legs” (which are the spider’s front legs). They look flexed and ready to jump.

    Thanks for these spectacular photos and the interesting commentary.

  9. loren russell
    Posted July 27, 2017 at 9:27 pm | Permalink

    The first spider may be mimicking a Grey Alien [the species that does anal probes] rather than a frog.


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