Spider That Builds Its Own Spider Decoys Discovered


A spider that builds elaborate, fake spiders and hangs them in its web has been discovered in the Peruvian Amazon. 

Believed to be a new species in the genus Cyclosa, the arachnid crafts the larger spider from leaves, debris and dead insects. Though Cyclosa includes other sculpting arachnids, this is the first one observed to build a replica with multiple, spidery legs. 

Scientists suspect the fake spiders serve as decoys, part of a defense mechanism meant to confuse or distract predators. “It seems like a really well evolved and very specialized behavior,” said Phil Torres, who described the find in a blog entry written for Rainforest Expeditions. Torres, a biologist and science educator, divides his time between Southern California and Peru, where he’s involved in research and education projects.

“Considering that spiders can already make really impressive geometric designs with their webs, it’s no surprise that they can take that leap to make an impressive design with debris and other things,” he said.

In September, Torres was leading visitors into a floodplain surrounding Peru’s Tambopata Research Center, located near the western edge of the Amazon. From a distance, they saw what resembled a smallish, dead spider in a web. It looked kind of flaky, like the fungus-covered corpse of an arthropod.

But then the flaky spider started moving.

A closer looked revealed the illusion. Above the 1-inch-long decoy sat a much smaller spider. Striped, and less than a quarter-inch long, the spider was shaking the web. It was unlike anything Torres had ever seen. “It blew my mind,” he said.

Written By: Nadia Drake
continue to source article at wired.com


  1. Surely this is a learned cultural trait as opposed to any genetic coding or predisposition. Eeerie , I actually see this as unevolutionary. Are there brains sufficently evolved to even come up with this?

  2. Pauly,
    I’d be very very surprised if this was learned.  I am by no means a spider expert or even a spider person…. but lots of seemingly complex behaviors are, in fact, controlled by small batteries of genes and a few simple rules.  I do not know if this is one of those instances, but learning and culture in association with spiders seems far fetched.

  3.  Why do you assume that “this is a learned cultural trait” when spiders do not have a social organisation or a family from which to learn anything? A spider constructing a web is not operating from learned behaviour & this decoy [if that is what is is] is merely an elaboration of the principle of the extended phenotype. The complex mating behaviour of bower birds doesn’t depend on bower bird culture or socialisation [ok it’s no doubt refined with practise], so why should spiders be different?.

    P.S. What amazes me is the behaviour of the octopus given the short lifespan & no cultural transmission. I wonder often if we humans over-rate the advantages endowed by planning, thought & society. It’s just our bias.

  4. Crooked Shoes,Michael Fisher
    I made the “learned” comment because this seems to have a reasoned and intelligent aspect to it. If this is being reported correctly and this is observed across the species and not just a random occurrence , then this does look to have some kind of cognitive inference built in. I understand that spiders are not exactly a complex social animal so the idea of culture propagation,given their life span and relative isolation, seems unusual. But the idea that evolution or the genetic genes stumbled onto this, seems equally unintelligible.

  5. Why assume that this simulacrum is intended as a decoy? Perhaps spiders have evolved to the point where they’ve discovered religion, and these things are little representations of the arachnoid deity they’ve elected to worship. After all, this sort of thing is not unheard of in the arthropod kingdom:


  6. Pauly_ Surely this is a learned cultural trait as opposed to any genetic coding or predisposition. Eeerie , I actually see this as unevolutionary. Are
    there brains sufficently evolved to even come up with this?

    Given that many spiders are cannibalistic and fairly short lived, it is unlikely that any spider learns from other spiders.

  7. Yeah I’ve said that but you got to say its unusual. There’s always usually an explanation , Are the spiders in-fact desperate for socialization and weave a spider in web form. Like Tom Hanks and Wilson in Cast Away:) 

  8. Or the spider is weaving from a shadow outline projected onto its web. In some ridiculous way…
    Has to be something like that,has to be. They are obviously mimicking something unintelligbly

  9. Mr. Dawkins, I know it has been thoroughly refuted (and having read The Extended Phenotype, I understand why), but seeing this, Lamarckism springs to mind. Your thoughts please.

  10. Here’s what I think: A spider sitting on an immaculate web is an easy
    target for a [bird?] predator. A ‘dirty’ web with pieces of leaf &
    fly wings stuck to the web will increase the chances that a bird strike
    will be against a piece of flotsam & jetsam rather than the spider

    I don’t know if any spiders habitually clean their webs of prey bodies or just go off & build a new web, but suppose that some mutation of the spider in generations past resulted in a spider that realigned the detritus caught in its web to form a large attractive target for bird predators.

    In later generations of this spider it might have been a pay off to add legs to the decoy ‘spider’ ~ bear in mind that the decoy spider ‘legs’ are bits of stuff glued to threads of the web. The web is the scaffolding for the decoy ‘spider’ legs.  You will notice that the decoy ‘spider’ is symmetrical, but building symmetrically is a spider behaviour so attaching detritus to the web in a symmetrical pattern would be natural.

    Just sayin as the modern argot goes… 🙂

  11. If the purpose of this artificial spider is to confuse or distract predators, as both the article’s author and Jerry Coyne maintain, then I don’t understand why its creator chooses to animate it by jiggling the web. This action is clearly intended to draw the attention of something, and unless this is the first non-human example of a practical joke, what reason could there be for the faux arachnid’s designer to make this preemptive display?

    The decoy idea just doesn’t wash, so I wonder if it might not have something to do with attracting a mate. Lady spider is walking along, is in the mood for amore, spots this big, sexy spider, goes to investigate, then Geppetto spider comes up from behind and gives her the business. This seems a more plausible explanation than the birdstike theory.

    Edit: I’ve just realized that this is also a decoy idea.

  12. A few other hypotheses:
    – to deter other animals from damaging the web accidentally? (ie. they see the big spider, realize a web is there, and avoid the web)
    – territorial display? To fool other spiders into thinking a larger spider has made the web, so they are detered from attacking or building their own webs too close.
    – sexual display? Similar to bowerbirds, it is a construct to show the spider’s genetic superiority to the opposite sex.

    The thing that bothers me is that usually a spider web is designed to be almost invisible in order to catch prey. By putting a huge spider in it, wouldn’t that scare off potential prey?

  13. I’ve got it, its obvious , the spider obviously secretes something in its shape from its extremities to its core. Maybe the female. And the weaving around this secretion is simply reflex.

    All the spider is doing is tracing the secretion , like a child would trace a picture with tracing paper and a pencil.

  14. I’m particularly impressed that they seem to be able to count…at least to 8 in any event.


    A few other hypotheses:

    territorial display? To fool other spiders into thinking a larger spider
    has made the web, so they are detered from attacking or building their
    own webs too close.

    When there is a territorial dispute between spiders, the loser usually gets eaten by the winner!  Webs can be taken over by other spiders who have eaten the previous owner.

  16.  No need for a dichotomy here as the two causations are not really in opposition.

    As Matt Ridley puts it,

    ” Nature via nurture. “

  17. Suppose a long time ago there was a little spider that produced an egg with a mutation. The new spider had the odd habit of making knots in its web. And his descendants also. Predators sometimes captured such a knot in stead of the spider. So the spider had a bigger chance of survival than its siblings. Some descendants made bigger knots and survived better. Sometimes later the knots got little pseudo feet. And so forth, and so forth…
    Tomorrow I’ll tell you another story.

  18. The things is, how does it know how it looks like to clone itself ? ( Please, early morning stares at raindrops or dew while shaving doesn’t count )

  19. Everyone!!!!
    This is awesome.  Exactly what science does.  A new phenomenon is observed and scientists (and scientifically minded people) brainstorm to develop hypotheses.  Hypotheses compete and testable hypotheses are tested (experimentation)…..  Things that are false drop out of the discussion and a clearer and clearer picture develops.

    I am rooting for the “they learned it on the Ark” hypothesis.  I know, I know, it is impossible to test.  But, I heard about a guy who built a life sized ark (and from what I understand he built it precisely to biblical specifications).  I am going to lobby that we capture two of these spiders and let them loose on the new ark. When “ghost spiders” start showing up in every nook and cranny, viola — god exists!

  20. Given that it is newly discovered, scientists probably shouldn’t automatically assume that it operates within the same  behavioral parameters as all other known and studied types.

    If the female is, like some spiders, cannibalistic, it is possible that the male too is cannibalistic and preys on others of its own kind and sex and could, therefore be building the ‘decoy’ – IF that is what it is – to entice other males in, as the less competition there is for females the greater his chances are of breeding successfully.

    As regards whether the tactic is learned or innate, entomologists would have to take a closer look at the spiders environment to see how it, and its closer relatives interact with each other and their prey items. 

    Incidentally, the fact that this is in the ‘web news’ section of Prof. Dawkins site, is funny too.. 😉

  21. This is very cool.   But if the spider starts writing “SOME PIG” within its web, I might start rethinking the god thing.

  22. Oh you lowly mammals, having only two eyes truly makes you blind.

    This is an image of the Great Eight-Legged in the skies, praised be his silvery abode. Protector against the winged beasts, provider of bountiful catch. It is He who wobbles the great web of the Universe http://www.nature.com/nature/j

    FYI, you humans are just here to provide warm and dry nooks and crannies for some of our brethren. Don’t get any ideas.

  23. A spider that builds extra web has evolved to the point where the extra web built resembles, among other things, a spider. They do this for no reason at all but it has the byproduct of allowing greater survival rates among those that build spider resembling webs.

    Spiders that, for no reason at all, built webs that resembled cheeseburgers, have all died out and thus are not available for study.

    There is no craftiness or intention going on here at all. And, though the web may decoy predators away, they are not actually built as “decoys”. The web is not actually “meant” to do anything, they just happen to have the byproduct of confusing or distracting predators; which is probably how they evolved to the point they have.

  24. It seems the additions to webs is common in this genus of spider, and for some reason improves the insect catch in those webs.  There are are various suggestions on the link about how this might work.

    What are the functions of the stabilimentum?

    Various theories have been propounded as to the effect of the stabilimentum: strengthening the web, preserving the web by causing birds to avoid it, even attracting insects (although it would be natural to think that the more solid-looking stabilimentum might make the webs easier for insects to avoid).

    The spider we saw makes it into a “decorated” hiding place, but that is most likely an embellishment by this one species upon a structure originally serving other purposes.

    In 1998 I-Min Tso, now a professor at Tunghai University in Taiwan, did a field study with Cyclosa conica (the spider we photographed) to find out whether “Stabilimentum-Decorated Webs Spun by Cyclosa Conica (Araneae, Araneidae) Trapped more Insects than Undecorated Webs”.

    He was able to make the comparison because where he worked (near Pellston, MI), the spiders sometimes omitted the stabilimentum (and 18 out of 24 webs with stabilimenta had no prey included in the “decoration”).
    This seems odd, as the stabilimentum with prey is cited as a characteristic of the genus Cyclosa, but maybe other observers have failed to notice instances of C. conica webs that lack the stabilimenta, or lack the wrapped prey within them. 

    At any rate, Dr. Tso found that webs with stabilimenta caught more prey than plain webs even when the plain ones were larger. 

    Similar results have been found for other species that add stabilimenta to their webs. – http://nosleepingdogs.wordpres

Leave a Reply