An unusual antipredator defense

December 16, 2013 • 8:38 am

Yesterday, reader Roo sent me the Torygraph‘s photo of the day, which is an assassin bug. The caption is below (I’m not sure why they use the past tense):

These ruthless Assassin bugs hid from potential predators using a camouflage cloak – made from the bodies of ants they had killed. The deadly insects paralysed the ants by injecting them with a toxic enzyme before sucking them dry. They then piled the dried-out corpses on their sticky backs to act as a defence against other predators, such as jumping spiders. Picture: Guek Hock Ping/Photoshot/Solent News

Picture 1

Note that assassin bugs (unlike “ladybugs,” which are beetles in the order Coleoptera) really are bugs : they’re in the order Hemiptera, or “true bugs.” (If I want readers to learn anything from this site, it’s to use the word “bug” properly!) They’re also in the order Reduviidae, some of whose New World species—probably not the one above—carry the protozoans that cause Chagas disease, an often asymptomatic but sometimes fatal illness. For many years people thought that Darwin had been infected with Chagas on his Beagle voyage, accounting for his frequent and lifelong bouts of illness, including malaise and vomiting. We’ll never know for sure, for doctors have suggested many other causes, ranging from simple nervousness to the latest Darwin-illness fad, cyclical vomiting syndrome.

Assassin bugs are so called because they stick their snout (“rostrum,” if you want to be technical) into the prey, injecting a saliva that liquifies the prey’s insides. They then suck it dry.

It’s interesting to speculate how this evolved. This adaptation (and who can deny that it is one?) involves both a morphological trait (a sticky back) and a behavioral trait (the tendency to put the husks of your prey onto your back). Without that sticky back, you have no initial advantage, so I suspect that the evolution of this mimicry began simply because the bug had a back that could adhere to dead insects, perhaps because of cuticular lipids that served other functions, like desiccation resistance or attracting mates. Perhaps a prey accidentally adhered to one of the bugs with a particularly sticky back, and that individual gained an advantage, as it was simply harder to attack and eat. This would give an advantage to genes producing not only stickier backs, but also  promoting any tendency to place sucked-out prey on your back.  I am curious whether the ant carcasses are inherently sticky too—as they appear to adhere to each other—or whether the bug actually puts something on them to help them stick together.

But this is all speculation. What is on firmer ground is the idea (still probably not demonstrated through experiment) that this is a remarkable adaptation to deter predation. I wouldn’t call it “mimicry” (unless predators avoid piles of dead ants), for this ant-covered bug isn’t really deceiving the predator by “pretending” to be something else. It’s simply making it harder for predators to grasp and eat them.

66 thoughts on “An unusual antipredator defense

  1. The behavior might rather be aimed at fooling ant prey. Smelling like ants might make the bug a “stealth” predator, allowing it to avoid eliciting ant anti-predator responses.

    1. Just like when the humans used pieces of zombies draped around themselves to escape zombies in The Walking Dead.

      Yep, I took it low brow. 🙂

    2. There’s a ant-hunting spider that does this. It kills an ant and then “wears” it into the nest so that the other ants won’t attack it (while it’s killing them).

      1. The spider must trick the dying ant not to emit the “holy crap, I’m in trouble” pheromones before killing it or the other ants would catch on.

        1. I’m not sure exactly how it works, it was a TV show that I saw a few weeks back. IIRC the spider also used its pedipalps to ‘wave’ the dead ant’s antennae back and forth when another and would touch it.

  2. That would be ‘family Reduviidae’ of course.

    Brilliant bug, though, it’s like it carries its safari trophy cabinet with it!

  3. My understanding of the word bug, as a non-native-anglophone, is ‘any small creepycrawly with too many legs that can’t look you in the eye’. All beetles and spiders may apply.

    1. That’s the colloquial use. Biologists have a more restricted definition, sometimes using the term “true bugs” for clarity.

      Both of these are expansions of the initial coinage ca. 1620, which was used to refer to bedbugs specifically, a pest that was widespread then and is making a return in the US now.

      1. Biologists are entitled to their specialized technical usage. They’re not entitled to insist that the rest of us are using it improperly.

          1. What about all those bugs the FBI, CIA, NSA use?

            When I took entomology years ago I learned about the “Homoptera” but Wikipedia informs me that: “Homoptera is a deprecated suborder of order Hemiptera; recent morphological studies and DNA analysis strongly suggests that the order is paraphyletic.” So I’m glad I got that straightened out.

        1. I agree that worrying about the common-name use of “bug/true bug” is pedantry, and I wish the enforcers would just stop — if you know and care enough about the groups in question, you find it easy and simple to say “hemipteran” [or “homopteran” — also true bugs unless you’re a true beliver]. I think I knew the proper names for insects orders just about the same time I got the first few dinosaur genera, stars/constellations, and minerals. Probably was 7 or 8 yo then..

          1. Thanks for calling me a pedant and an enforcer, and telling me how to behave. Some of us biologistscare about accurate terminology (the misuse of “epigenetics” has bunged up a lot of discussion), and, by the way, you learn something if you know that there are different orders of insects and that ladybugs are really beetles.

            It would be polite for you to apologize for dissing the host now.

            1. Jerry, I am normally a descriptivist when it comes to usage, and while I appreciate your motivations I would think your efforts doomed to failure, a noble linguistic lost cause the likes of who/whom.

              However, given your victory over the LA Museum “God quote” sign, I say go for it. 🙂

    2. The Woodland Park zoo here in Seattle has an indoor exhibit that defines “bug” as creatures in the order Hemiptera… and yet the exhibit contains beetles and spiders and is called “Bug World”.

      Honestly, I’m OK with the more lax definition, which basically includes any terrestrial arthropod. Scientists will use the taxonomic term for disamiguation anyway.

    1. Yes, that may be part of it. However, ants are full of formic acid and I think they don’t taste too good to most predators.

    2. From the annals of 1980s elementary school humor comes the theory that predators are distracted by the “Pink Panther” theme song. (Dead ant, dead ant, deadantdeadantdeadant…)

  4. “They then suck it dry…. It’s interesting to speculate how this evolved. This adaptation (and who can deny that it is one?)”

    David Dobbs might argue that, if your parents really sucked, then you would suck even more. But he’d just be projecting.

  5. After reading many comments from this website I would like to state that I have ZERO biology experience, and so, my hypothesis (I hope I’m using that word correctly) may be way off base. Please correct me if/where I am wrong.

    Couldn’t the “assassin bugs” also have evolved this morphological trait from slower increments? Where the back of the bug which genetically had a spot where the body of the ant “hooked” onto it. This advantage was passed down and from that trait the smooth and “sticky” back evolved in order to keep the ants’ bodies onto the back of the bug.

    Is this biologically possible? Or am I completely on the incorrect biological path?

  6. It seems so ghoulish – sucking your prey dry then piling their carcasses up on your back and parading around with them. The insect world makes for good horror; no wonder horror movies often take inspiration from them (the anatomy for Alien for example, I believe was inspired by dragon fly nymphs).

    1. If you enjoy a good dose of terror & despair I recommend the four-part SciFi book series known as the Hyperion Cantos of which Hyperion is the first volume.

      The Assassin Bug is a rank amateur compared to The Shrike ~ a biomachine with an unknown [in the first book] agenda. The author, Dan Simmons, draws on numerous influences including Teilhard de Chardin, John Keats & Norse Mythology. A thoroughly unpleasant antidote to saccharine xmas cheer.

      The book is divided up into intertwining novellas which tell the stories of a number of pilgrims travelling together to meet their fate on the the planet Hyperion. Not a barrel of laughs. I loved it. 🙂

      You need to get stuck into that Goodreads list dear!

      1. That sounds great! I have a habit of watching dystopian movies, especially when sick. Once I watched The Road during one sick episode which resulted in bizarre dreams.

        1. It’s cheaper entertainment than magic mushrooms. The Road [film] is a bit Disney compared with my recommendation ~ which requires patience & reflection to fully savour the misery…

  7. this ant-covered bug isn’t really deceiving the predator by “pretending” to be something else.

    I’m not so sure. My first thought was that it looks like a mama spider with a bunch of spiderlets on her back.

  8. I wonder whether the ants’ “death pheromones” or other alarm chemistry might be involved here. Would the pile of carcasses serve to attract other ants responding to chemical signals from the dead? If so the bug would not need to expend as much energy in hunting prey, while lugging around carcasses.

    1. I was wondering that in the spider comment. I wonder if the ants don’t get a chance to emit the pheromone. Do ants come running to help with said “holy crap” pheromone or do they run away?

  9. It’s simply making it harder for predators to grasp and eat them.

    It strikes me the dead ants might form a sort of ablative or sacrificial armor. When a predator bites or grabs at the assassin bug, he will instead come away with dead ant husks. These can then be replaced by the assassin bug with its own prey.

  10. All these naturalistic explanations may well be off the mark. What if (insert favorite deity here) ordained that this insect must wander the earth cloaked in the wages of its sinful predatory behaviors in the vein of Jacob Marley’s chains? In this way, other insect may properly shun it.

    Thx for posting this. The natural world never ceases to feed our sense of wonder.

  11. This is a nymph, either of the genus Paredocla or Acanthaspis; I call them “backpack bugs”. They live in Tropical Africa. Having a sticky back is not all that uncommon in Reduviidae nymphs, sticking ants on them is. The benefits of this HAVE been experimentally investigated!!!
    First, Brandt & Mahsberg (2002) in “Bugs with a backpack: the function of nymphal camouflage in the West African assassin bugs Paredocla andAcanthaspis spp.” showed that it certainly has an anti-predatory effect. Several other publications have since come out, including a mention in Gullan&Cranston’s “The Insects – an outline of entomology, 4th edition” pp. 369-370. Not only do predators like junping spiders attack a backpack-carrying bug less frequently and does it allow for easier ant-hunting ambushes, it also quickly detatches when a predator grabs it – not unlike a lizard’s tail.
    Having handled these bugs myself, I can say they’re weird. First, it’s hard to distinguish even what subphylum you’re dealing with as they walk very fast and look like tiny hermit crabs. Then they’re hard to grab because you are soon left with a packet of dead ants while the bug scurries away. Seriously awesome evolutionary marvels!

    1. It would be interesting to know exactly which aspect of this behavior deters spiders from attacking. Is it the smell of the ant corpses? The resemblance to baby spiders? The sheer bulk of it? Or what? Would piling up any sort of debris on the bug’s back have a similar deterrent effect?

      1. And given that other related species also have sticky backs, what kinds of stuff end up stuck to them?
        Maybe just whatever happens to settle there: sand, dust, bits of leaves and twigs could work just as well, and they get the same advantages of camouflage and ablation.

  12. One is tempted to ask how long “assassin bugs” of the order Reduviidae have been living this lifestyle. It would be fascinating to hear of any fossil evidence.
    Polish palaeontological journals might be worth consulting. Cue Hili.

    1. Not sure about reduviid history (yet), but Poland has at least one excellent palaeontological journal that is always worth consulting, and can be consulted by anyone with an internet connection because it has always been fully open access.

      No match for Reduviidae at APP, but there is this in a newer and more famous open-access journal:

      “Reduviidae are relatively old, with one fossil that has been attributed to the Reduvioidea (Reduviidae + Pachynomidae) from the Early Jurassic and three reduviid specimens from the Early Cretaceous … [However,] Fossils that can be reliably classified to subfamily, tribe, or genus are predominantly from Dominican and Baltic amber (Miocene – Eocene) and offer little insight into the evolutionary timing of major lineage diversification events within Reduviidae.”

      1. This months APP – the email table of contents came out a couple of days ago – contains an article on a 1868 (IIRC)- discovered fossil, reassigning it to the Reduviidae. The rocks are of 61 +/- Myr old (middle-lower Paleocene), adding a good 5-10 million years to the group’s antiquity.
        The paper contains stuff about the identification of Mullerian mimicry which goes over my entomological knowledge. You seem to be better informed on such matters, so Prof Ceiling Cat is likely to thank you for your comments on this.
        Citation : “Wasp mimicry among Palaeocene reduviid bug from Svalbard
        Torsten Wappler, Romain Garrouste, Michael S. Engel, and André Nel
        Acta Palaeontologica Polonica 58 (4), 2013: 883-887 doi:

        Link to the paper :

        1. Thanks Aidan, it didn’t come up on Google Scholar or the search of APP’s own site, being so new.
          I’m no entomologist, but the evidence or discussion of actual mimicry in the Wappler et al. paper looks a bit thin to me. Apparently the authors are aware of various cases of waspy-looking extant assassin bugs, the Svalbard specimen was previously identified as a wasp wing but has diagnostic reduviid features, and they infer that wasp-mimicry was established by the time those rocks were laid down; but it’s a single wing, and who knows what the rest of the animal looked like?

          1. but it’s a single wing, and who knows what the rest of the animal looked like?

            So, some poor schmuck has got to be paid to go back to Svalbard and spend weeks searching through acres of snow-covered scree for more samples, dodging polar bears every so often.
            [SELF ; standing at back of room, waving hand in the air, shouting “me! me! me!”]
            I was wondering if there was something buried in the family names or the naming-of-parts which described the mimicry. But if you can’t see it either …

  13. To me it looks like a blackberry on legs! (I accept, though, that that may not be how it is perceived by the spiders and other predators that may have supplied the selective pressure for the evolution of this trait).

  14. Back in the spring I spotted (and photographed) what I now think was a lacewing larva on my deck. They have the same behavior, in that they take the carcasses of their prey, and stack them upon their backs. I figured this was a one of kind of behavior as I had never heard of it, I was wrong.

    There is just something creepy about a species with that kind of lifestyle. After reading up on the lacewing I found that they have very stiff hairs on their backs for impaling their victims, but beyond that I have to think one would need to be quite nimble to continue with the stacking. Does anyone know of a video or a description anywhere showing or describing this behavior?

  15. Putting aside the gruesomeness of these little creatures, you’ve just got to admire the cleverness of the adaptations that are reflected in their behaviours. No engineer could have come up with these perverse inventions… which brings to mind again Orgel’s Second Law, “Nature is cleverer than you are”. Or perhaps there is a corollary to that law i.e. “No matter what gruesome behaviour you can possibly conceive of, nature can come up with something more gruesome”

  16. The picture of this creature has me wondering how intellectually challenged dolts like Ham, Hasslenut and the Woopster would marvel at their god’s inventions.

    I’m fairly confident that the response they’d offer as to why their god may have created mosquitoes capable of infecting their god’s favored species would be the same.

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