Bombardier beetles in action, escaping toad digestion

I’ve only scanned this new paper from Biology Letters (reference and free access below, pdf here), but it’s a report involving one species of the famous bombardier beetles, comprising over 500 species in four “tribes” of the family Carabidae in the order Coleoptera (beetles).

They all secrete a hot and toxic spray from their abdomens, resulting from the mixing together of two sequestered compounds, hydrogen peroxide and hydroquinone. This mixing produces a chemical reaction that not only heats up the mixture to near the boiling point, but produces a gas that violently expels the noxious spray from the abdomen, driving away predators. Here’s a Attenborough video of one driving away a praying mantis:

Bombardier beetles are beloved among creationists, who claim that there’s no way this system could have evolved without killing the beetle. (They apparently claim that the evolution of this process, which produces results only after the two chemicals are in place, would require foresight on the part of natural selection, which it doesn’t have.) But scientists have produced plausible step-by-step scenarios for the evolution of the process: see one scenario here.

The spray not only drives away predators, but can even protect the beetle after it’s eaten. The new paper shows that the species studied, when ingested by toad predators, can not only live for two hours in the toad’s stomach, but can force it to vomit by squirting. The beetle comes out covered with toad-stomach slime, as in the video below, but none the worse for wear. Here’s the paper’s abstract, which is easy to understand.

Some prey animals can escape from the digestive systems of predators after being swallowed. To clarify the ecological factors that determine the success of such an escape, we investigated how the bombardier beetle Pheropsophus jessoensis escapes from two toad species, Bufo japonicusand Btorrenticola, under laboratory conditions. Pheropsophus jessoensis ejects a hot chemical spray from the tip of the abdomen when it is attacked. Although all toads swallowed the bombardier beetles, 43% of the toads vomited the beetles 12–107 min after swallowing them. All the vomited beetles were still alive and active. Our experiment showed that Pjessoensis ejected hot chemicals inside the toads, thereby forcing the toads to vomit. Large beetles escaped more frequently than small beetles, and small toads vomited the beetles more frequently than large toads. Our results demonstrate the importance of the prey–predator size relationship in the successful escape of prey from inside a predator.

But of course you want to see this in action, so here it is (don’t watch right after dinner!):


Sugiura, S. and T. Sato. 2018. Successful escape of bombardier beetles from predator digestive systems. Biology Letters, online, Feb. 7, 2018. DOI: 10.1098/rsbl.2017.0647



  1. loren russell
    Posted February 13, 2018 at 2:44 pm | Permalink

    Not just toads — Here we have the great Charlie D reminiscing on his beetle collecting days at Cambridge:

    “I will give a proof of my zeal: one day, on tearing off some old bark, I saw two rare beetles, and seized one in each hand; then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth. Alas! it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as was the third one.”

    The one in his mouth was surely a carabid. Given that there are several Brachinus in
    England, and all pretty rare, my bet is that Darwin got “bombarded”

    • Brian salkas
      Posted February 13, 2018 at 3:48 pm | Permalink

      This is among my favorites of Darwin’s antidotes. It is also a call for optimism for those of us who are a bit disorganized or absent-minded but still curious about the workings of the natural world around us.

      • Posted February 13, 2018 at 5:07 pm | Permalink

        Nice Freudian slip there! (anecdote).

        • Brian salkas
          Posted February 13, 2018 at 10:50 pm | Permalink

          that’s my phone slipping up there. turns out auto-correct is no anecdote for typing mistakes.

    • Posted February 13, 2018 at 4:01 pm | Permalink

      Now see here, that’s the advantage of having zippered pockets!

  2. GBJames
    Posted February 13, 2018 at 2:44 pm | Permalink

    Maybe that’s how Jonah got out of the whale’s belly!

  3. ThyroidPlanet
    Posted February 13, 2018 at 2:47 pm | Permalink

    It has such a creationist allure, doesn’t it?

    A dazzling show, obviously reactive chemicals. I suppose they could point at snake, scorpion venom too – to try to make a point…

  4. glen1davidson
    Posted February 13, 2018 at 2:53 pm | Permalink

    Some foods are just terrible for causing heartburn.

    Glen Davidson

  5. Posted February 13, 2018 at 2:54 pm | Permalink

    Of course, we sometimes ingest bugs that make us vomit after a while too. I don’t suppose such bacteria and viruses consider that a good thing like the bombardier beetle does. Ok that’s way past my anthropomorphism limit for the day.

  6. loren russell
    Posted February 13, 2018 at 3:17 pm | Permalink

    Every time I’ve had the opportunity to demonstrate bombardiers, naive observers immediately dub them “farting beetles” for the audible “ffft, ffft, ffft”! By kids of all ages. Somehow that epithet never makes it into textbooks.

    Don’t have them in the Willamette drainage of western Oregon, but I’m planning a trip to the Rogue in a few weeks. I should roll some rocks for a fresh supply.

  7. BobTerrace
    Posted February 13, 2018 at 3:20 pm | Permalink

    The UNtasty!

  8. rickflick
    Posted February 13, 2018 at 3:29 pm | Permalink

    Poor little guy. Two hours in the stomach of a toad. It’s kind of biblical somehow. I think it’s a delightful creature.

    • Posted February 13, 2018 at 5:05 pm | Permalink

      I’m waiting for Ken Ham to say Jonah had this property too.

      But I do have some concerns about the ethics of making a toad swallow one of those f###ers.

      (WWPSSS — What would Peter Singer say?)

      • loren russell
        Posted February 13, 2018 at 6:06 pm | Permalink

        The toad had no choice, while the experimenter had, eer, no choice.

        No does Peter Singer, I suppose..

  9. Brian salkas
    Posted February 13, 2018 at 3:33 pm | Permalink

    (“They apparently objection is that the evolution of this process, which produces results only after the two chemicals are in place, requires foresight on the part of natural selection, which it doesn’t have.)”

    I think this is a typo in an otherwise fascinating post.

  10. Adam M.
    Posted February 13, 2018 at 3:42 pm | Permalink

    Richard Dawkins had a nice segment on the bombardier beetle during episode 3 of his 1991 Christmas lectures, Growing up in the Universe:

    It starts at around 50:30 in. The whole lecture series is well worth watching.

    • Adam M.
      Posted February 13, 2018 at 3:43 pm | Permalink

      Hmm, the embedded video starts at episode 1 and you’ll have to use the button at the top-left to choose episode 3 (which is fourth in the list).

  11. Posted February 13, 2018 at 4:43 pm | Permalink

    I guess injury or infection could produce the reaction inside the beetle’s body, like our pancreatitis.

  12. Ken Kukec
    Posted February 13, 2018 at 6:12 pm | Permalink

    Craftiest bombardier since Yossarian served with the 256th Squadron in Italy.

  13. Christopher
    Posted February 13, 2018 at 6:24 pm | Permalink

    Fascinating videos, dreadful music! What on earth was it about bombardier beetles or toads made the producer of the second video think that crap techno electronic “music” was the way to go?!

  14. eric
    Posted February 13, 2018 at 8:03 pm | Permalink

    Poor mantis! But cool biology.

    • David Coxill
      Posted February 14, 2018 at 12:09 am | Permalink

      If it could speak it would say something like
      “HOT HOT HOT “.

  15. David Coxill
    Posted February 14, 2018 at 3:57 am | Permalink

    The two chemicals involved are similar to T Stoff ,used by the Germans together with C Stoff to make a rocket fuel ,or i might be wrong .

    • infiniteimprobabilit
      Posted February 21, 2018 at 2:56 am | Permalink

      Similar but not precisely the same, according to the Dawkins link posted by Adam M at #10.

      The bombardier’s blast is hydrogen peroxide + hydroquinone. But apparently the hydroquinone plays no part in the reaction (though I guess it adds to the toxicity of the spray). Apparently it’s the H2O2 plus a catalyst that causes the blast.

      The T-stoff was indeed hydrogen peroxide, the C-stoff (methanol-hydrazine) was a fuel, e.g. in the Me163. This combination was notorious for its tendency to explode if you gave it a dirty look. Other rockets used T-stoff plus a catalyst Z-stoff which is possibly a closer analogue to the bombardier.


  16. Posted February 14, 2018 at 4:22 am | Permalink

    I’m now imagining the toad equivalent of a lads night out after a few beers, daring each other to have a try of the hottest curry available and seeing who can keep it down the longest.

  17. Florian
    Posted February 14, 2018 at 4:51 pm | Permalink

    Years ago the fundamentalists parents of my girlfriend, knowing i wasn’t much of a believer and was more interested in science, gave me a book explaining how the bombardier beetle was proof evolution was false as it was impossible for such a beetle to have evolved without exploding itself in the process. I wish Why Evolution Is True had existed back then.

    • Posted February 15, 2018 at 11:40 am | Permalink

      It has been a common creationist trope for a long, long time.

      I seem to remember it was one of the first things I ever saw on – 1994 or 1995 I think.

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