A most bizarre and mysterious cocoon

August 29, 2013 • 9:53 am

by Matthew Cobb

This bizarre photo was posted the other day on reddit’s “whatsthisbug” subreddit by Decapod73, with the following information: “Seriously, who makes egg cases like this? Just under 2cm across, Southern Peruvian Amazon”

The various suggestions in the discussion include moth/not moth, harvestman/not harvestman. No one has an answer so far.

Decapod73 says that s/he initially thought it was an ermine moth caterpillar that had started making a cocoon but then got distracted. But then more of the damn things started turning up… Cue creepy music.

Heres one on the underside of a tarpaulin, also by Decapod73 (this was posted a couple of months ago):

So. Ideas anyone? In particular, has anyone from Peru seen this kind of thing before? My guess is a small moth, but I think we need not only an ID, we also need an explanation for the “fencing” – is it to keep out predators? Are there other examples of fences in nature? And why the maypole? Is that again to deter ants or whatever?

Here’s something similar, a moth (?) cocoon that was photographed by Randy Emmit in 2011 that was spotted here by elijrus and linked to on the reddit page thing (I don’t know the correct reddit nomenclature). It looks like there’s an ant stuck in there, but it isn’t clear.

h/t @phil_torres on twitter

90 thoughts on “A most bizarre and mysterious cocoon

  1. I don’t think that it’s from a moth – it doesn’t look anything like any moth cocoon I’ve ever seen.
    The second thing, I would say, is almost certainly a cocoon of a braconid(?) wasp – the black shrivelled bit would then be the remains of the caterpillar.

    1. I think it looks very much like a moth cocoon, and the black shriveled bit would simply be the caterpillar’s last shed skin. Braconids usually don’t devour their hosts that thoroughly.

      1. Well, I can’t say for sure, but I’m still quite convinced it is a wasp cocoon, although braconid was more of a guess, and could be completely off.
        I’ve seen quite a number cases where wasp larvae have left hardly anything but the head capsule and a tiny bit of shrivelled up skin next to cocoons looking very similar to this one. What makes it more tricky is, that the outer rings may have well been spun by the caterpillar, before being killed by the wasp larva from inside as a prepupa.
        Also, while the picture is too low res to be sure, when zooming in a lot it looks like the black shrivelled bit is actually spun into the fuzzy silk around the cocoon, so it would have to have been there before the cocoon was finished.
        A higher res version of the picture would probably be needed to clarify this.

  2. Do any silk-producing creatures other than spiders build complex, precise structures? I don’t think I’ve ever seen a silk structure this complex that wasn’t created by a spider.

  3. It almost looks more like the fruiting body of a fungus than a cocoon.

    I wonder if it’s a form of camouflage.

  4. I really hope someone posts an explanation, otherwise I might be compelled to spend hours trying to determine the right search terms for Google Images.

    1. Yeah…me three. LOL. This would scare the shit out of me if I found it out and about. I’m more jumpy too since I just watched ‘Dark Skies’ and the Greys terrify me even though I don’t believe they are real. If you want a good scare – that movie was well-done.

  5. Nah, it’s a yurt with an antenna and fencing to keep the cattle from straying. The photos were taken by NASA.

    1. Because you’ll probably just find eggs or a pupa and that isn’t helpful. However, if possible, putting a jar over the one on the tarp may be the way to go to catch whatever eventually emerges.

    2. The person who posted the pictures to reddit went back to the US and posted the pics once he got back. No internet where he was outside the US.

    3. May I make a suggestion? Why not tear one open and see what’s inside?

      Yeah – I believe many a Stephen King short story has started just this way.

  6. I wonder what the strands that go from the fence to the cocoon are for. They look like the strands spiders use to sense motion in their webs, but if the little guy is pupating, he can’t very well leap out and gobble up an intruder.

    1. I’d guess that those are structural supports, like guy wires, to help hold up the “fence posts”. Which is all kinds of awesome.

    1. Now we are getting somewhere. Your suggestion looks closely related to the mystery animal, unlike all the other suggestions so far (including mine).

    2. The thing is, however, that moths generally (I can’t think of any example to the contrary right now) have cocoons that are at least in some way elongated, while the thing in the first two pictures looks almost perfectly round. Also, the silk in there simply doesn’t look “mothy” to me, it much more reminds me of the fluffy, cotton wool like silk in some spider egg cocoons.

      1. I agree. I think the resemblance to Bucculatrix is entirely superficial; the actual cocoon within a Bucculatrix “fence” is always an elongate, longitudinally ribbed structure. Spider egg sac, or possibly some bizarre neuropteran, would be my guesses.

  7. Clearly, it is a white chocolate Hershey’s Kiss. Surrounded by some new ad gimmick to be revealed later.

  8. The Open Univerity here in Britain has a website called ISpot where you can place photos and use the wisdom of crowds to help identitify aspects of the natural world.

    I don’t have the skill to work even the most simple copy and paste, but if anyone here fancies having a go, maybe we could get a positive identification.

    1. Thank you for that! I’ve often thought there should be a place for the wonderful and bizarre “wtf”s we stumble upon in nature!
      Here is your link:
      Great stuff!

      On another, and entirely off-topic note, I soooooo want to submit my idea for a reality show where they round up the most hopelessly technologically challenged group and pair each one with a professional competitive computer gamer. Each coach has 6 weeks in which to impart as much knowledge and skill as possible, and then set them loose in a final competition – with an audience and giant screens and everything. I often think about this when I am trying not to strangle my coworker – whose technological ineptness is one for the record books. Three times yesterday I had to explain that no, she was not “booted out of the program” but had actually clicked the window BEHIND the program she was using. That was just 3 times yesterday. I can’t tell you how many times I address this same problem with her on a monthly basis. I don’t think she is capable of understanding the difference between the desktop, os, and browser. She’s not otherwise unintelligent (except she’s very religious), and she’s in her early 60’s…but that’s no excuse. My own mother reformats her computer about once a week (that’s a problem on the other end of this spectrum). Ok…/endrant lol. Sorry to hijack. It’s late and I’m bored!

      1. My husband, who’s a scientist with Big Pharma, has a standard response every time the ID guys tell him he “really should” learn X about the software, etc: “OK, I’ll work on that as soon as you learn to synthesize your own drugs.”


          1. I should clarify, being that your husband actually works in a lab, that by “mouse” I don’t mean the kind with fur and whiskers. Rather quite the opposite of uneventful, clicking on that type of mouse might in fact result in a bit of surprise on all parties involved.

            1. Ha, ha!

              Ironically there are not only no mice, there are scarcely any beakers or Bunsen burners. Think large computerized machines paneled with blinking LEDs. He can handle any of those in his sleep; unless it involves Windows…


              1. Bah! If I spent all those years to become a scientist, I would want not only the white lab coat, the bunsen burners and beakers, a mouse, but also jars full of pickled mystery parts. And a DeLorean. And the mouse would be my friend and come to work with my in my lab coat pocket. Ssssh! Possibly mad scientist hair too. Why isn’t “Lab Chic” ever a style fad btw? Doesn’t Big Pharma create mutated manbearpig cyborgs for the military? Or am I thinking Area 51?

          2. Actually, he is fairly electronically challenged. 😀 But the kids and I bail him out when we can. Of course, as long as there are no problems or upgrades he putters along OK with his company-issue ThinkPad.

            One of the eye-openers re the computer age is the real time lost to simply keeping up. No wonder corporations are loath to update; each significant change requires company-wide training sessions. A tremendous loss of productive person-hours.

            1. This I know. We are a small business and recently underwent a whole point of sale/inventory management software change. It was and is painful even though it was so long overdue. The old software was basically created by jewelry store owners who happened to do a little programming on the side. (www.winjewel.com – just the website alone says it all). We would have monthly reports of inventory on hand where it looked like $75,000 in jewelry was unaccounted for. The next month we would have a bottom line surplus of $48,000. Being that inventory is my responsibility, and items weren’t actually disappearing and reappearing through a glitch in the matrix, this was beyond maddening. The new software is sooo much better but we are still having growing pains, and of course the added stress of retraining my coworker. The loss of productive person-hours indeed.

              Somewhat on topic, because I have again hijacked this post, we have a spider mystery at work. In the mornings before we wipe down all the glass cases, we might come upon a bit of very fine powder that is perfectly detailed like a small spider. All that remains is white powder, no hairs or anything – just a dime-sized bit of spider-shaped powder. I will take a picture next time – but has anyone else seen this?

              1. Look up — I think your ceiling is dropping little white bits of plaster or paint, that create dry splatter patterns when they land.

            1. I do tech support for my organization, and when I get calls I wish I had the nerve to answer the phone with “Hello, IT, have you tried turning it off and on again?”.

              Because honestly that would fix 90% of the issues.

              1. Even when I start by telling tech support, “I am an experienced user. Bump me up to the next level,” I still get: “OK, it says you are experiencing problems. Are you sure your computer is plugged in?” “Thank you. Can you turn your computer on..” etc.

                So feel free to tell then turn it on and off. We’re used to it.

              2. Tulse – Isn’t that the best? I am comfortable with technology – my inept coworker calls me the techno guru. I am absolutely nothing of the sort. I just don’t let it intimidate me. I was called into work on a Saturday because their internet was down. Of course the first tech asks me to make sure the router is plugged in. I told him I checked but I really didn’t, because of COURSE the router is plugged in. Who would unplug the router?? Well, about 15 min later you can imagine my embarrassment when I finally have to fess up that yeah…there really are no blinking lights of any sort on the router and yeah – it’s f’ing unplugged. I’m sure the tech guys would have much rather had a total newb than someone just comfortable enough with technology to be arrogant. IT Crowd is brilliant. One of the best has to be when they let Jen borrow THE INTERNET for her presentation.

                Gould – LOL – I am so impatient having to go through that whole bit – but due to the story above, I’ve been rather humbled since.

  9. I remember someone working on opilionids that made stockades when I was on Barro Colorado – the males used them as amphitheatres when courting females. Never saw them myself, though – too much field work of my own to do.

  10. Reblogged this on BugTracks and commented:
    I’ve never “reblogged” something before, but several people have forwarded this to me, asking for my thoughts on it, and it does seem like something that belongs on BugTracks. I’m afraid I don’t have the answers, but here are my thoughts: The resemblance of the structures in the first two photos to the silk “fence” built by ribbed cocoon maker moths (Bucculatrix spp.) is entirely superficial. Bucculatrix spp. never have horizontal webbing between the “pillars” of their fences, and more importantly, the cocoon in the middle is elongate with longitudinal ribbing. Almost all other moth cocoons are more or less elongate. Among insect cocoons, this most reminds me of some kind of neuropteran (see, for instance, the spongillafly (Climacia) cocoon on the cover of my book. Although that cocoon is somewhat elongate like a moths, other neuropterans (e.g. green lacewings and antlions) make nearly spherical cocoons, and neuropterans in general typically have some kind of outer silken structure beyond the cocoon itself. However, I have a hard time picturing the spire at the top of this “cocoon,” and the delicate silk strands anchoring it to the substrate, being made from within. Therefore, I think it’s most likely that these are spider egg sacs, which are constructed from the outside and are usually not oblong like moth cocoons.
    The object in the third photo is oblong like a moth cocoon, and I’m pretty sure that’s what it is. The black thing stuck to the left side of it would be the caterpillar’s shed skin. It looks very much like a tent caterpillar (Malacosoma )cocoon, but I’ve never seen one with gauzy concentric rings like this. In the blog where this photo was first posted, it is explained that the cocoon was found under the cover of a bee hive, so rather than being a stand-alone “fence” as in the first two photos or a Bucculatrix cocoon, these outer layers were spun between two boards.
    Anyone have anything to add?

    1. I have a hard time picturing the spire at the top of this “cocoon,” and the delicate silk strands anchoring it to the substrate, being made from within.

      Excellent point — the structure really does seem to require construction from the outside, so it must be a repository for eggs, and not a cocoon.

  11. I’ve been thinking about this, and to my practical eye, it does seem clear that at least the central part is constructed from the outside. As has been pointed out, the central spire could not be constructed from the inside unless it were first suspended and then attached during the process of constructing the conical base. However, it extends seamlessly from the base. Also, the threads under tension between the spire and the surface could not have been placed from the inside.

    But what I’m now wondering about are those complex, loose, springy threads between the posts on the perimeter. Those look like something a spider does. Would a caterpillar have the necessary equipment to do that?

    Anyone have any further news on this? My curiosity is killing me!

  12. I’m a writer, not an arachnologist, so don’t take this suggestion too seriously, but this structure reminds me of the lampshade webs made by Hypochilus spiders. It seems more refined and more organized, but I can imagine possible functions for the various substructures based on how seemingly similar substructures function in lampshade webs. William Shear wrote this, one of the major papers on this type of web: http://psyche.entclub.org/pdf/76/76-407.pdf

  13. This looks more like a trap than a cocoon to me. My intuition on insects/arachnids tells me it was definitely made by a spider by process of elimination:

    * The cocoon is too small to be a moth (in comparison to the surrounding structure).
    * It is highly unlikely to be a wasp because it is far too spherical. Every wasp cocoon I’ve ever seen/read about/seen pictures of is elongated.
    * It is not a fungus because, well, a fungus cannot make such connecting structures with such air gaps.

    Here’s why I think a spider made it:

    * It definitely appears to have been weaved in a complex circular pattern that is the hallmark of spiders.
    * The mixture of more than one kind of silk (only spiders can do that–that I’m aware of).
    * The spires of the surrounding structure look like they’re made up of the sticky kind of silk that spiders can secrete.
    * It looks like a TRAP! As in, if a bug goes in it isn’t supposed to be able to get out. Such bugs would be provide great sustenance to emerging baby spiders.
    * Spider cocoons are often very round like that.

    Now for some wild speculation: I bet that there was a thread connecting the maypole to the ground at one point. Why? That would allow a small amount of electricity to run through the structure. No idea what it’s purpose would be (kickstart egg development?) but if you hooked up one end of a sensitive multimeter to the maypole and stuck the other end in the ground you’d definitely register a few millivolts. At the cocoon site this would result in oxidizing of the cocoon and potentially, an oscillation effect in the web–turning it into a weak antenna (extremely so).

    1. My co-author, Catherine L. Craig, and I were looking at these photos yesterday, and we are pretty sure that they were made by spiders, mostly for the reasons you cite. We both think the spider is cribellate, but that’s as near as we can get to an ID (well, that narrows it down to a close relative of more than 10,000 known species; I suppose that counts as progress given there are more than 42,000 known spider species).

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