A spider that mimics a beetle

Matthew Cobb sent me another remarkable case of mimicry, revealed in this tweet:

The link leads to an article on the Arachne.org.au site that gives this information under the heading “Coccorchestes ferreus Griswold, 1984 Beetle Mimicking Salticid”

This jumping spider is one of the most unusual of the jumping spiders found in Australia, having over time successfully adapted by mimicking a beetle. Many subtle and obvious features of the beetle have been assumed. This must have protected this genus and its species (mostly found in New Guinea) from predators, allowing its survival as a group. The specific name is from the Latin, ferreus, meaning of iron. The female body is shiny dark brown to black, body length to 3mm. The male was not known to Griswold in 1984 but has since been documented in Davies and Zabka 1989.

Note that “allowing its survival as a group” may be true, but selection was surely on individuals, not on groups (as the post could be taken to imply). There are other spiders in the genus that appear to mimic beetles.

Other views from the post:

32 Comments

  1. Posted May 5, 2017 at 10:08 am | Permalink

    I wonder if the beetles mimicked are prey items?

  2. Posted May 5, 2017 at 10:16 am | Permalink

    Thanks for sharing the photo, really different this spider. 🙂

  3. rom
    Posted May 5, 2017 at 10:27 am | Permalink

    What’s the advantage for the spider? I would guess that the world for spiders is primarily tactile and chemical rather than visual? Is the beetle a less desirable prey?

    Just curious.

    • darrelle
      Posted May 5, 2017 at 10:55 am | Permalink

      Jumping spiders are somewhat rare among spiders in that they have very good eyesight. They are ambush hunters that rely on their visual capabilities.

      Their two primary eyes are highly specialized and very large. They are somewhat like a telescope in form in that they are cylindrical (or conical) with a large lens on the outer end and the receptors (eye piece) at the other end, deep inside the head. And they can move them, though they do it differently than most animals do. The outer surface of the eye doesn’t move. Instead the end that is deep inside the head moves. There are some really cool video clips in which you can see this as lighting changes in the eyes as the spider looks around

      Some years ago researchers discovered that jumping spiders are capable of sighting prey at a distance, planning a route from their location to the prey and then following the route even when they can no longer see the prey. This was surprising because it was thought at that time that the spiders’ brains were not large enough to perform the computations necessary to do that. It eventually inspired new ideas about how to improve robotic vision systems using less computational resources.

      • rom
        Posted May 5, 2017 at 4:11 pm | Permalink

        Thanks; does not quite answer my question. What advantage does the mimicry endow? Its prey is unlikely to know it looks like a beetle?

        • darrelle
          Posted May 5, 2017 at 5:06 pm | Permalink

          Sorry, I can’t answer your main question. Just your question about spider vision. This kind of spider can see well.

          I doubt there has been enough study of this spider to definitively answer your main question. Likely reasons.that have been seen in other species have been mentioned by other commenters here.

          • rom
            Posted May 5, 2017 at 6:38 pm | Permalink

            OK thanks
            WBenson in post 4 has some ideas
            rom

  4. W.Benson
    Posted May 5, 2017 at 10:33 am | Permalink

    Your comment about adaptations not being directed to group survival is well taken. Spiders, contrary to the opinion of many city dwellers, are neither loathsome nor dangerous to many large predators, and may be important prey to visually hunting animals, ranging from birds to wasps. On the other hand, hard-shelled beetles probably offer little nutrient reward when eaten and, being smooth and slippery, may be fumbled and dropped during a predator attack. Small spiders that look and behave like the beetles could benefit if predators treat these beetles, even if they are not bad tasting, as unworthy prey.
    There are probably other ways the resemblance could come about, and experiments are needed.

  5. Posted May 5, 2017 at 10:39 am | Permalink

    The spider that spectacularly mimics the ladybug is easy to understand because the ladybug is aposematic. But this looks like a garden variety beetle. What is the advantage in mimicking that, I wonder? Perhaps to fool the spider’s prey?

    • Paul Schoeckel
      Posted May 5, 2017 at 12:58 pm | Permalink

      I was wondering if this was an offensive or defensive adaptation.

      • loren russell
        Posted May 5, 2017 at 1:11 pm | Permalink

        Really, it could be either defensive or offensive, or both. There are a fair number of Coccorchestes spiders, and they vary enough in size [mostly 3-6 mm — typical salticid range], color [usually dark body, but some quite metallic], texture, and marking [mostly leg/tarsus color] to suggest that they are tracking different models. NO one seems to hae identified a particular model, but it’s likely either weevils or leaf beetles seem likely — perhaps both, depending on the spider species. Weevils aren’t commonly poisonous, but may be too well-armored for some predators, while many leaf beetles are quite toxic………..

        To add to the fun, underneath the beetle like appearance [or Darth Vader appearance for C. ferreus], there’s an unusual range of structural variation. That, and the occurrence of Coccorchestes in Central America — unexpected for an otherwise Australasian genus — suggests that there’s been convergence onto this form of mimicry by quite distantly related salticids.

        So there’s much to learn, and much to wonder about. Enjoy this diversity while it lasts, folks.

  6. darrelle
    Posted May 5, 2017 at 10:58 am | Permalink

    Even given the top view the giant primary eyes led me to guess jumping spider.

    Very cool! Jumping spiders continue to amaze.

  7. Posted May 5, 2017 at 11:18 am | Permalink

    I don’t understand why some people seem to be so attached to the idea of group selection. It’s bizarre.

    • Posted May 5, 2017 at 11:46 am | Permalink

      Mimicry, to me, is a good example of why group selection doesn’t work. You can ask yourself, why do so many species mimic a bad-tasting model rather than evolve a bad taste themselves? The answer, I think, is the latter would require group selection. If a gene arises in an individual of species A causing the individual to taste bad, the individual might get spat out but the predators will not start avoiding species A in general because the rest taste fine. The bad taste gene won’t spread. However, a gene for mimicking a bad-tasting model will deter predators and can spread.

      • Posted May 6, 2017 at 12:58 pm | Permalink

        I disagree. Following this logic, no animal or plant would ever develop a bad taste unless co-selected for another trait. I also disagree with the question “why develop adaptation A instead of adaptation B”. Adaptation development is limited by mutations that appear in a population randomly. Hence, evolution does not follow the optimal design.

        • Posted May 6, 2017 at 1:38 pm | Permalink

          I tend to think that the “limited by mutations” excuse is a non-explanation, but you might be right that unpalatability is adaptive to deter predation. I just can’t come up with a good story that does not involve group selection. The same might be said of aposematism, like warning coloration, I might add. In that case, the mutation would seem to potentially harm the individual by making it more conspicuous to predators. I was hoping PCC would enlighten me.

          • Posted May 7, 2017 at 2:49 pm | Permalink

            I see “limited by mutations” all the time. To take the simplest example, where is our photolyase gene now? It would be so useful to us, especially to white people, but once our ancestors lost the gene, mutations will never produce it anew to be selected. Same with gulonolactone oxidase.

  8. Posted May 5, 2017 at 11:34 am | Permalink

    Amazing, but one wonders why mimic a plain looking beetle. I don’t know, but maybe as others have suggested it could be so they are ignored. It is like a form of camouflage

    • loren russell
      Posted May 5, 2017 at 3:52 pm | Permalink

      The beetles, and so their mimicking spiders, would not be “ignored” by small vertebrate predators [small birds, lizards, frogs] if they were both edible/nontoxic and returning enough nutrients to be worth the catching and processing. So blending with the crowd doesn’t help you if someone is hovering the crowe. As I noted above, chrysomelid [leaf] beetles are the likely models for Coccorchestes species, and many of these beetles are toxic, usually taking up toxins from the foliage they eat. Some, but not all of the toxic leaf beetles display aposematic colors. Perhaps the aposematic colors are unnecessary if predators learn that beetles on a particular tree are nasty.

      Beyond that, someone simply has to do the natural history. Unless some lucky museum coleopterist to find a Coccorhestes or two pinned in a series of dead-ringer beetles, or some archnologist studying Coccorchestes gets a vial that’s mostly beetles.

  9. David Duncan
    Posted May 5, 2017 at 11:36 am | Permalink

    Spelling error alert! Did you mean “tw**t”? 🙂

  10. Michael Fisher
    Posted May 5, 2017 at 11:37 am | Permalink

    Off Topic [ish]

    I was listening to a BBC Radio 4 programme on the element mercury & there was an especially interesting bit on how excess mercury [due to us humans] travels up the chain to birds via spiders. Spiders hoovering up insect prey by the ton & themselves being eaten by birds…

    Spider questions…

    Are they all carnivores?
    Do any species of spider hunt in packs in the way of ants?

    • darrelle
      Posted May 5, 2017 at 1:28 pm | Permalink

      There is the very interesting jumping spider Bagheera kiplingi that appears to have a mostly herbivorous diet. Most of its diet consists of the “specialized protein- and fat-rich nubs called Beltian bodies” that form at the leaf tips of the acacia plant. They also eat nectar, the occasional ant larvae and the occasional other B. kiplingi.

      I don’t know of any spiders that hunt in packs but there are social spiders that live in colonies cooperatively building and maintaining webs to catch food. According to Wikipedia there are 23 species scattered among 11 genera and sociality evolved independently perhaps as many as 18 or more times in spiders.

      • Michael Fisher
        Posted May 5, 2017 at 7:07 pm | Permalink

        @darrelle Thank you! At first I thought you were pulling my leg [Bagheera & Kipling], but I’ve looked it up since. It seems nobody is sure how this little wonder ingests plant matter given that spiders in general tend to suck up the liquidised internals of their prey…

        Shame about the pack hunting – I wonder why ants, but not spiders?

        • darrelle
          Posted May 5, 2017 at 7:15 pm | Permalink

          That species name is enough to make one wonder if it is a joke. One of the fun perks of a biologist is coining cool names.

    • W.Benson
      Posted May 5, 2017 at 5:28 pm | Permalink

      Almost all spiders are carnivores. An exception is the jumping spider Bagheera kiplingi, which feeds in part on structures produced by Acacia trees, Beltian bodies, that the trees ‘use’ to feed protective ants. Here is the reference:
      http://blogs.discovermagazine.com/notrocketscience/tag/beltian-bodies/#.WQz7FNLyvIU

      Some web-building spiders form social groups in which members cooperate in subduing prey. I’ve never heard of a spider that hunts in packs.

      Birds eat many spiders.

      • W.Benson
        Posted May 5, 2017 at 5:32 pm | Permalink

        Darn. I’m just repeating what darrell wrote.

        • Posted May 5, 2017 at 6:45 pm | Permalink

          Repeating the fact that no spider hunts in packs made me feel better. 🙂

          • darrelle
            Posted May 5, 2017 at 7:11 pm | Permalink

            LOL!

  11. Posted May 5, 2017 at 12:11 pm | Permalink

    Interesting question – is the mimicry for protection from predation or for camouflage while hunting? Protection seem less likely in this case. Are there any other cases of hunting camouflage going to this extreme mimicry?

  12. Richard Bond
    Posted May 6, 2017 at 4:27 am | Permalink

    Obviously, whatever is being fooled cannot count. It reminds me of a certain scene in The Hitchhiker’s Guide to the Galaxy:

    Hotel receptionist: “Who do you think you are? Zaphod Beeblebrox?”
    Beeblebrox: “Count the heads!”

  13. Posted May 6, 2017 at 1:04 pm | Permalink

    This spider, to me, looks like a beetle with a homeotic mutation!

  14. Tony Eales
    Posted May 9, 2017 at 5:02 pm | Permalink

    Wow! New bucket list species to photograph


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