Ants build a hanging, living bridge to raid a hornet’s nest

This one-minute video comes with no information about the location or the species of ant, clearly raiding a hornet’s nest for grubs.  What puzzles me is how they built the damn bridge.  If they started on only one side, they’d have no way to go upwards when they reached the bottom. They could start on both sides and join at the bottom, but why, if they wanted to access the nest, did they need a bridge in the first place? Why couldn’t the ants just walk directly to the nest on the ceiling? After all, they seem to cling to the ceiling, at least around the nest, pretty well.

And why did the chain go so low?

I sent the video to a friend of mine who works on ants, and he was mystified as well. Given the lack of notes about the video, he helpfully identified the ant as a New World army ant in the genus Eciton, a denizen of Mexico and South America. They’re known for their raids on wasp nests, and love to abscond with the wasp grubs (you can see that in the video).

But as for why this bridge exists, neither of us knew. So we jointly formulated a theory, which is ours. This was, perhaps, an experiment done by some naturalist, who put a piece of thread in a catenary shape from the edge to the nest to get the ants to crawl along it. But why didn’t the ants just walk directly to the nest along the ceiling? Well, the experimenter could have coated the space between the roof edge and nest with Fluon®, a slippery, Teflon-like substance that insects can’t get a grip on. They would then have to go along the preexisting thread (not visible in the video) to get to the nest. There would be no Fluon on the house side of the nest, explaining why ants are on the ceiling in that area

That’s just one hypothesis, but it’s the only one that makes sense to me. The idea that this was some kind of experiment is also supported by the fact that the video notes have no information in them, nor does the site allow comments.

As for how these ants defeat the wasps, I’m not sure, but this is their lifestyle, and they regularly raid nests like this.

If you have another theory which is yours, by all means put it below.

24 Comments

  1. Posted October 28, 2020 at 2:41 pm | Permalink

    I think you’re right. I bet there is a rope core to the bridge. (In fact, I think I can see it in the video.) Otherwise it would be too heavy for the ants to hold.

    • GBJames
      Posted October 28, 2020 at 2:48 pm | Permalink

      There may be a thread in there but I don’t think the ants need it for strength. Those little things are incredibly strong for size and very light weight.

  2. Posted October 28, 2020 at 2:47 pm | Permalink

    (Appreciative of the little Monty Python nod there)

    Your theory makes sense (and I did wonder about this too when I first saw this video), but it occurs to me that there could conceivably be an advantage to attacking the nest from beneath. It might possibly mess with the wasps’ navigation: perhaps they can’t see the grubs being taken if it’s happening below the entrance of the nest. That would make sense if the wasps are primarily guarding against attacks from above (which they might easily do)

  3. EdwardM
    Posted October 28, 2020 at 2:50 pm | Permalink

    I saw this before but can’t find it now. The ants DID walk over the ceiling to the nest, using their bodies as a track for others to walk on. But as more and more ants climbed along the track made of their colony-mates, it pulled off the ceiling. More ants came to join the fun and the mass of the ant bridge grew and it sank lower and lower.

    At least that’s how I remember it, but ding-dang it, I can;t find it now.

    • Posted October 28, 2020 at 3:25 pm | Permalink

      I heard from an army ant expert who says that your theory is basically correct. If I get permission to post his explanation, I’ll put it above. Watch this space.

    • Posted October 28, 2020 at 4:53 pm | Permalink

      Yes, this was what I thought too. For this to be correct it also must be that a single ant finds it difficult or impossible to walk upside down across the ceiling. If it was easy, they would take separate parallel paths to the wasp nest as we see ants do on a surface where they can stand on their own six feet.

    • ThyroidPlanet
      Posted October 28, 2020 at 8:04 pm | Permalink

      Oh I see now – naturally forming a catenary!

      So is the observed shape a true catenary? That is elegant and fascinating!

  4. ThyroidPlanet
    Posted October 28, 2020 at 2:53 pm | Permalink

    Intriguing ideas

    I suppose the ants could pick up odorants/pheromones from the hornets…

    The pre-existing catenary idea makes sense for this instance – as in, how would the bridge shape be controlled to be a shape that by definition forms by gravity pulling a fully formed object (string) down to a resting state?

    Now as usual, as my comment is complete, I’ll actually watch/read the video/article.

  5. Ken Phelps
    Posted October 28, 2020 at 3:07 pm | Permalink

    Godidit.

  6. Mike
    Posted October 28, 2020 at 3:08 pm | Permalink

    I wonder if an ant itself can cling to the underside of a smooth surface like that ceiling (to get to the nest), but an ant carrying a huge wasp larva can’t cling to a smooth surface and needs something grippy like other ants (to get back from the nest).

  7. Charles A Sawicki
    Posted October 28, 2020 at 3:29 pm | Permalink

    It seems that a string is present, since this sort of structure has only strength to resist extension (not bending). No way for them to connect the 2 end points unless they could form 2 long hanging chains (possible) and then make them swing until they contacted (seems very unlikely, but a very interesting adaptation if they could accomplish it).

  8. C.
    Posted October 28, 2020 at 4:11 pm | Permalink

    My immediate thought was that they did start on the ceiling but as more and more joined in, gravity did it’s thing and they began to droop into the catenary, which a previous comment had suggested. Either way, this is just one damn cool video and I’m sure glad it happened where it would be appreciated rather than attacked with a can of Raid.

    • Torbjörn Larsson
      Posted October 28, 2020 at 7:45 pm | Permalink

      That view was my own before-reading-comments idea as well – and I think I have seen it in some video – so add me to the consensus.

      Since we will have an explanation (or not) posted tomorrow, I won’t dig further tonight.

  9. Posted October 28, 2020 at 5:05 pm | Permalink

    We have an answer from an expert on army ants. I’ll put it in a separate post tomorrow morning.

  10. Posted October 28, 2020 at 5:24 pm | Permalink

    That is pretty impressive, even so. I don’t know how the wasps fight back. Maybe they just leave, with the queen.

  11. Eddie Janssen
    Posted October 28, 2020 at 8:03 pm | Permalink

    Where are the hornets? Aren’t they supposed to defend their nest?

  12. Posted October 28, 2020 at 8:08 pm | Permalink

    “Ants build a hanging, living bridge to raid a hornet’s nest”

    Upon first seeing this, it reminded me of the U.S. political situation we’re now in. If ants can figure out a way, hopefully, we can.
    Good luck to us on Nov. 3rd.

  13. Jonathan Wallace
    Posted October 29, 2020 at 5:10 am | Permalink

    Looking forward to tomorrows expert explanation!

  14. Posted October 29, 2020 at 6:16 am | Permalink

    Can ants carry grubs upside down? I doubt it!

  15. ThyroidPlanet
    Posted October 29, 2020 at 7:59 am | Permalink

    What is the best estimate for the average army ant mass? How about force of their cohesion in Newtons… This will make a great puzzler…

  16. ThyroidPlanet
    Posted October 29, 2020 at 8:06 am | Permalink

    A likely structure under the ants is an electrical cable – perhaps connecting to an ice melting apparatus on the roof… connected to power behind the soffit doubt that’d be to code…

  17. ThyroidPlanet
    Posted October 30, 2020 at 9:45 am | Permalink

    Weaver ants forming a bridge across a small gap : https://youtu.be/A4uv27nSaH4


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