More mimicry: beetles mimic flies

August 10, 2012 • 8:40 am

The panoply of mimetic plants and animals in nature is endless, and scientists are always discovering more cases.  A really cool one is described in two papers cited below, summarized by Morgan Jackson in his Biodiversity in Focus website, from which I’ve taken the pictures (they’re from the second paper cited below, one that I cannot access).

I have read the Hespenheide paper, which you can dowload for free, and it describes a group of diverse Neotropical beetles with an unusual pattern: their head and front part of the thorax is red, the rest of the thorax is black, often marked with white to yellowish stripes, and the tips of the “elytras” (hardened wing covers) are golden yellow to pale gray.  Hespenheide describes at least 60 species of beetles in five families that have this pattern.  Here’s one example from the Vannin and Guerra paper, which I’ve taken from Jackson’s post that describes this single species:

Here’s a shot of the species in the wild; as the Hespenheide paper points out, these beetles (like their presumed models, which we’ll get to in a second) tend to sit on tree trunks.  These are all beetles:

Looks like a fly, doesn’t it?  And both papers suggest that this is the evolutionary force that gave rise to the beetle pattern: it’s mimicking a fly: a sarcophagid flesh-fly for the beetle shown above. Here’s a picture of a sarcophagid fly:

The mimicry’s pretty good, isn’t it?

Now there are several reasons for this mimicry. The fly, for example, could be distasteful or poisonous, and birds could learn to avoid its pattern.  A tasty beetle, by evolving to resemble that pattern, could enjoy some protection from sharp-sighted bird predators that have learned to recognize and avoid it. That’s called Batesian mimicry.  Alternatively, both beetles and flies could be distasteful/dangerous, and evolve to resemble each other because having a common pattern facilitates predator learning, conferring extra protection. That’s called Müllerian mimicry.  Neither of these seem applicable in this case because flies simply aren’t distasteful to predators (mostly birds).

Both authors, however, suggest a different explanation—actually a variant of Batesian mimicry.  The likely solution is that flies are simply hard to catch for birds—even entomologists with big nets have trouble nabbing flies (ask me!).  Studies show that flies are rare in bird stomachs compared to other potential prey. Both authors, then, suggest that bird predators simply learn to avoid going after flies because they’re hard to catch, and the reward is unlikely to match the futile effort.  Once a bird has learned to avoid catching flies, then any beetle (mimic) that looks like a fly (the model) would also be avoided. That’s the selective pressure on the beetle to accumulate mutations that make it resemble the model.

Now this could be tested: one could expose a naive bird to flies, watch it go after them, fail miserably, and then expose the bird to the mimicking beetles. It would presumably then avoid the beetles.  However, birds that hadn’t been exposed to flies, and thus hadn’t experienced dipteran-related failure, would go after the beetles more readily.  These kinds of tests have been done with other kinds of mimicry, and succeeded remarkably well. They haven’t, however, been done with these insects.

Nevertheless, the explanation is a good one, for the mimicry is so obvious, and it’s just another marvel that we lucky evolutionists get to read about every day.

If you’re a strict creationist, you should ask yourself why God would make a beetle look just like a fly.  One could always answer, I suppose, that it pleased God to do so, or that His ways are mysterious. But that’s the end of the questioning. The evolutionary hypothesis leads to predictions, including the experiment I suggested above.  Another is that beetles that mimic flies should live in the same areas that flies do, and encounter the same potential predators. That’s not a necessary prediction of the God Hypothesis.

h/t:Matthew Cobb


Hespenheide, H. A. (1973). A novel mimicry complex: beetles and flies, Journal of Entomology Series A, General Entomology, 48 (1) 55. DOI: 10.1111/j.1365-3032.1973.tb00034.x

Vanin, S.A., & Guerra, T.J. (2012). A remarkable new species of flesh-fly mimicking weevil (Coleoptera: Curculionidae: Conoderinae) from Southeastern Brazil Zootaxa, 3413, 55-63. PDF Available Here

20 thoughts on “More mimicry: beetles mimic flies

    1. Good ways to tell the difference:

      1. The beetle’s actual eyes are black, and are clearly visible on the photo.

      2. The beetle’s legs are considerably more robust than a fly’s legs.

      But those details may not be obvious without a close inspection that a predator may not make. It’s clearly a case of “see no weevil”.

      1. Acute abdominal pain. Fainting. Loss of feeling in extremities. Doctor tole me “Don’t worry, it’s just a pun.”

  1. Have there been any studies involved in where the ‘boundary’ of successful mimicry lies in a similar prey/predator relationship (bird/insect?) Seems to be fodder for creationists in that they would contend the beetle would need most all the favorable mutations at the same time (large colored ‘eyes’, striped thorax, ‘winged’ abdomen, ‘jerky’ movements) to fool the predator.

    1. But you can find species today showing every level of mimetic accuracy, if you walk in a diverse place like a tropical forest. Some butterflies have perfect fake eyespots, complete with fake reflections, on their wing trailing edges, to fool birds into attacking the wrong end. Other butterfly species have crude spots there; still perhaps sometimes effective, but not as convincing as the more elaborate ones. Give them a few hundred thousand or a few million years and they will improve.
      Recently I have had some flies come into my house that looked and acted like hornets. The neatest thing was that each wing had a small but conspicuous notch on its trailing edge, so that it gave the impression of being two overlapping wings on each side. That is a brilliant trick, because flies (“Diptera”) always have two wings, while hornets have four. This notch is surely going to get more conspicuous over evolutionary time. Eventually this fly’s descendants will fool even the most taxonomically-savvy bird.
      The world today is full of half-way adaptations, the living “missing links” whose fossils will be found and studied by future paleontologists (of whatever species takes our place).

      1. Indeed. It’s all about relative fitness. Mimicry doesn’t need to be perfect, it just needs to be good relative to the other individuals in the population.

        “Why are you tying your shoes? You’ll never outrun that lion.”

        “I don’t need to outrun that lion. I just need to outrun you.”

  2. This is exactly the kind of post I search for when I log into this site: Picture, results, citation, my take on this. Bang. Bang. Bang. Bang. I really don’t learn anything from the posts about mythology because I figured that out when I was 6.

    I am only a geologist, but am fascinated by evolution, so I need a biologist to filter these case histories for me. You do a good job.

  3. Now this could be tested: one could expose a naive bird to flies, watch it go after them, fail miserably, and then expose the bird to the mimicking beetle. It would presumably then avoid the beetle.

    This assumes there’s no genetic component to the bird’s behavior, and that each individual bird must learn for itself to ignore (not avoid) unprofitable prey. Wouldn’t the Baldwin effect apply here, with natural selection picking up at least some of the burden of learning? Birds with a predisposition to ignore fly-like prey would outcompete those that waste resources chasing such prey.

  4. Since God is well known to have “an inordinate fondness for beetles,” it seems likely to me that He just wanted to give the beetles a bit of a leg up versus the predatory birds.

  5. Reblogged this on macrocritters and commented:
    Hi all,
    I am travelling right now and won’t have much time to write for a couple of days. In the meantime I thought I’d share this excellent post on the blog “Why Evolution Is True.” It isn’t specifically about photography, but it has some great photos and mimicry is always a fascinating topic!

  6. Dear colleagues,
    despite the striking coloration pattern and obvious flesh-fly resemblance, this fascinating new species is probably involved in the so called “evasive mimicry”. This mimicry system is based on agility of the models, not on their palatability. In effect, flesh-flies must comprise a hard to catch group of prey. However, this kind of mimicry is still unexplored and there is no study demonstrating evasive mimicry unequivocally in nature (Please see: Ruxton, G.D., Speed, M. & Sherratt, T.N. (2004) Evasive mimicry: when (if ever) could mimicry based on difficulty of capture evolve? Proceedings of Royal Society of London B, 271, 2135–2142). Evolution is unquestionable for sure, this theory helps us to formulate testable hypothesis on this case. However, we must be cautious using this case as an example of mimicry, simply because many pieces of this puzzle still wait to be put together. That’s a lot of work to be done before we could confirm the reasons weevils mimic flies, I guess.

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