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Saturday, February 21, 2009

On Spider Intelligence

A few days ago, Tim Eisele put up another marvellous post, this one about window flies. It discussed insect vision and had this tidbit.
for small arthropods like insects, everything they see is something that we would consider to be a “macro shot”. And on top of it all, they are highly size-limited, they can’t have the honking huge lenses that we use on our cameras and microscopes for looking at things close up. For the smaller insects, like these, their whole eye has to be on the order of the size of a pinhead. So, how can they do it?

Some other arthropods, like spiders, basically can’t do it. They do the best they can with simple eyes (a single lens, and an array of light receptors to make an image), but even the best spider eyes are evidently low-resolution and what we would consider fantastically near-sighted. Which is why a lot of spiders pretty much give up on the whole “vision thing” altogether, settling for enough eyesight to basically detect light and movement, and letting it go at that.
That got me to thinking about spiders' brains. For example, is a tarantula smarter than a wolf spider or is it just the Costco-sized version of its little cousin? Here's a little bit I've discovered so far.

First off, back to the eyes. It turns out that jumping spiders can see pretty well.
The jumping spiders, Salticidae, are well known for their excellent eyesight. Their two AME eyes are greatly elongated and push deep into the animal's head. They work like a telephoto lens and have a movable retina to increase the visual field. Strangely they also have four layers of rhabdomeres. They are also known to be sensitive to four different wavelengths of light, 360 (Ultraviolet), 480, 500 and 580 nanometres. A jumping spider can distinguish objects at thirty to forty centimetres distance with its secondary eyes, once it is within about twenty centimetres of its prey it can see it with its AME main eyes.
They're an oddity in the arachnid world - like Tim said, most spider eyes are good only for detecting light and shadows. Back to the brain.

From the Arachnoboards comes this (spelling errors in the original, some corrections made).
When it comes to animals, other factors differ, like what proportion of the brain mass is made of connected neurons, is there any grey matter or the whole brain is only made of nerves intersections and nodes? In this regard invertebrates are way less endowed.

Finally, another key factor is how this brain is stimulated from the outside. Take two humans identical twins, have one live in a cell with no book or interaction or stimulus and you'll see that he won't measure up in any aspect to the one who grew up normally. Because of this, I would have a tendency to say that burrower Ts might be less stimulated since there is little intellectual stimulation when 90% of the living time is spent at the bottom of a tunnel where nothing occurs. On the other hand, an arboreal T has way more to deal with by simply wandering in the branches of a tridimensionnal tree, trying to analyse air movement to figure out if it's only a breeze or an airborne predator comming...
Going back to the spider anatomy discussed in the first link, we have this.


The nervous centre of a spider is situated in the prosoma. The central nervous system is compacted with the brain to produce a single mass of nervous tissue. This single mass can be divided into the lower star-shaped subesophageal ganglion and the upper spherical supraesophageal ganglion. A number of nerves arise from these ganglia and spread out to the body, making up the peripheral nervous system.

The supraesophageal ganglion can again be divided into the cheliceral ganglion and the brain. The cheliceral ganglion controls the musculature of the chelicerae, the pharynx and the poison glands. The brain is mainly concerned with association activities. It only receives information from the eyes, via the optic nerve.

Motor nerves that control the the legs and the pedipalps originate laterally from the subesophageal ganglion. Posteriorly the subesophageal ganglion gives rise to a set of nerves called the 'cauda equina' which pass through the pedicel to control the opisthosoma.
Imagine a central nervous system where all nerves and the spine as well is smushed into a single blob in your head and then radiate out from there. I think that's where the remark "the whole brain is only made of nerves intersections and nodes? In this regard invertebrates are way less endowed" comes in. The spider brain is then just a big switchboard with a tiny bit of intelligence for adapting to repeated stimuli. A bigger spider might have a bigger brain, but that brain might have the same intelligence as a smaller spider because the "switchboard" part is larger to deal with all of the added sensors across a larger body.

This is worthy of some more research. Thanks, Tim, for bringing to light another of God's wonders to explore!

Image used without permission from the Spider Anatomy page.

21 comments:

  1. Anonymous10:11 AM

    Thanks for the link! Regarding the jumping spider eyes, it is interesting to note that the "extreme distance" visual range for their "good eyes" is just about my minimum distance for comfortable reading with my nearsighted eye![1] (I just checked with a ruler, any closer than 20 cm and things get blurry).

    So, the spiders that are generally regarded as having the best eyes, still have vision that, in a human, would be considered severely nearsighted, and would require corrective lenses.

    The bit about the brain is interesting, the short distances evidently mean that it's easier just to send out a dendrite direct from what passes for a brain than to fool around with distinct nerves. We may not want to discount their actual intelligence too much though, I recall reading about a decade ago that personal computers were just then beginning to approach the processing power of an ant's brain. Given what a personal computer can do, that actually allows room for some significant smarts.

    -----

    [1] I have moderate "lazy eye", the right eye is nearsighted enough that I would need pretty good glasses if both eyes were like that. I use the nearsighted eye for reading, which my optometrist says is fine, because it means that I will probably never need to get bifocals. Yay!

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  2. Anonymous3:25 AM

    After searching for "spider intelligence" I found this interesting post. The other day I saw a very interesting behavior on a spider which left me intrigued.
    On the ceiling corner of my parent's bathroom was a daddy longlegs spider, and while I was in there, it walked along the ceiling, descended on its silk line, landing precisely on the tip of the water tap, drank a bit for a few seconds, then climbed the line back up into its corner.
    I was fascinated by this, and wondered how smart these little things really were...

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  3. Anon, that's really wild. Given how nearsighted the little guys are, how did he know the water was there?

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    1. Anonymous9:55 PM

      I was just reading an article about how ants consciously count steps, takes note of direction at all times, and use visual markers in the terrain while venturing outside the ant hill. I'm not positive, but pretty sure, a spider, being an uncolonized insect, would use these same navigational tactics just as well, if not better than an ant.

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    2. Anonymous9:56 PM

      This is a different anonymous person too, by the way.

      Delete
  4. Anonymous3:59 AM

    to the commenter, on computing power.

    10 years ago, the best personal computer could compute millions more instructions per second than an ant, which is beside the point. The PC is just hardware, you need to write software to simulate intelligence, 10 years ago, 20 years ago people have already written programs that simulate n+1 ants, it's reasonably trivial to do, plug in a bunch of rules and then a simulation progresses.

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  5. Anonymous6:22 PM

    Iv'e always been fascinated by the complexity of nature, and Iv'e also been observing spiders for a few months. When I saw the anatomy of a female spider (hypothetical of course)it struck me how complex these tiny things really are. It's truely amazing. Thanks for the help!

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  6. Thanks to both anons!

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  7. Anonymous7:09 PM

    RE: spider intelligence.

    I have some dwarf sunflowers in an outdoor wicker planter just to the left of a vertical wire cage with shelves I use for potting. About a week ago I noticed a triangular web touching two of the sunflowers, one side of the cage (at 90 degrees from the side of my house) and the side of the house itself. Down came the web. Well, as you can imagine, the web was up the next morning. Same place. Down again and for seven straight days the web came down and was back up the next day. I said to my self, OK, instinct, persistence and good spider "silk" capacity and that was it.

    Ok, so why am I posting this? Well, today, much to my surprise and delight, the far side of the web that was normally attached to the sunflowers was TWO INCHES away from the sunflowers! The away side was a little longer now, stretching from the side of the house to the wire cage. But there is absolutely no doubt that it was the intent of the spider to avoid the sunflowers. And thats not all. In order to make up for the loss of the
    square inch coverage of the web the spider had now placed another triangular web, for the first time, on the right side of the metal cage!

    This highly intelligent little spider.....has adapted and overcame!I suppose you might say well, he could have left and found a different place for his web. Still, his web will stay up and I will find him a bug or two. I figure he has 7 weeks before first frost. He has taught me an important lesson. He may have a tiny brain but damn, he sure knows how to use it! Good for him!

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  8. Anon, what a great comment! Thanks so much for stopping by and relating that story. It will make smile all day.

    :-)

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  9. Anonymous10:02 AM

    Update: the little guy from the previous post who redesigned his web: I've named him Leonardo S. (you know what the "s" stands for). I checked his website this morning. Leonardo has now constructed an addition to his web that reaches to the sunflowers. From a design standpoint this is very logical. With the foundation side secured Leonardo has now acquired a very considerable increase in web coverage with minimal silk expenditure. What impressed me was that this addition, constructed back to the sunflowers, did not come up immediately. Leonardo waited. Does this indicate patience? Perhaps even an application of logic and deductive reasoning? Not sure yet. Too early to tell. But, if the reader is familiar with applications of learning theory in the design of training simulations and programs it is a possibility. At least, for now, Leonardo's "interactivity rating" has gone up from a B to a solid A.

    This little experiment has taken a more serious turn. I was able to take down the web addition to the sunflowers without disturbing the main web which, as best as I can tell, is securely anchored. I am now keeping a log on Leonardo and checking his website at least twice a day.

    The next move is up to Leonardo. But, so far, he has given me more interactivity than some (internet) websites I've been on. So, I have high hopes for him but not really expecting anything close to what might confirm the possibility of reasoning.

    I've laid out some standards for an A+ in interactivity. First, if he keeps putting up the addition to the sunflowers..daily ... and I keep taking it down .. he has to stop doing this (for at least 24 hours)in less than 7 days. (This was how long it took him to stop the initial web connection to the sunflowers). Second, if he waits awhile (at least 24 hours) (and this is a long time in the life of a little spider) before the web addition goes up again, does it come up every day for awhile (at least three days running)(fixed schedule) or is it constructed intermittently (variable schedule)?

    Leonardo needs to meet both standards to get his A+ in "interactivity." If he does this then there is a possibility that his brain stem has the capacity (with a lengthy period of repitition and conditioning) for rudimentary reasoning.

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  10. The anon above returned and left the comment attached herein. Blogger is eating some comments of mine and unfortunately, this was one of them. Grrrr.

    Anon - you rock. Thanks for these great stories!

    -----------------

    Update: the little guy from the previous post who redesigned his web: I've named him Leonardo S. (you know what the "s" stands for). I checked his website this morning. Leonardo has now constructed an addition to his web that reaches to the sunflowers. From a design standpoint this is very logical. With the foundation side secured Leonardo has now acquired a very considerable increase in web coverage with minimal silk expenditure. What impressed me was that this addition, constructed back to the sunflowers, did not come up immediately. Leonardo waited. Does this indicate patience? Perhaps even an application of logic and deductive reasoning? Not sure yet. Too early to tell. But, if the reader is familiar with applications of learning theory in the design of training simulations and programs it is a possibility. At least, for now, Leonardo's "interactivity rating" has gone up from a B to a solid A.

    This little experiment has taken a more serious turn. I was able to take down the web addition to the sunflowers without disturbing the main web which, as best as I can tell, is securely anchored. I am now keeping a log on Leonardo and checking his website at least twice a day.

    The next move is up to Leonardo. But, so far, he has given me more interactivity than some (internet) websites I've been on. So, I have high hopes for him but not really expecting anything close to what might confirm the possibility of reasoning.

    I've laid out some standards for an A+ in interactivity. First, if he keeps putting up the addition to the sunflowers..daily ... and I keep taking it down .. he has to stop doing this (for at least 24 hours)in less than 7 days. (This was how long it took him to stop the initial web connection to the sunflowers). Second, if he waits awhile (at least 24 hours) (and this is a long time in the life of a little spider) before the web addition goes up again, does it come up every day for awhile (at least three days running)(fixed schedule) or is it constructed intermittently (variable schedule)?

    Leonardo needs to meet both standards to get his A+ in "interactivity." If he does this then there is a possibility that his brain stem has the capacity (with a lengthy period of repitition and conditioning) for rudimentary reasoning.

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  11. Anonymous5:48 PM

    An Update on Leonardo S. - Leonardo Does Housekeeping:

    Early October and leaves are starting to fall, blow around, swirl, etc. Leonardo's once pristine website is now painted in orange, yellow and brown. Fall must be a tough time of the year for little spiders. The shortened days are telling them winter is coming and they must get ready. Then there is the thick silk overcoat. And, if that wasn't enough - the ever blowing leaves are swirling into the web. For five days in a row I have checked the website. More and more leaves have piled up and the website is thoroughly trashed.

    AHA!. Something I caught for Leonardo. A nice, juicy fly. twwwanggg - the fly gets thrown into the center of the web. One very unhappy fly. But Wait ---- the fly has landed right next to a big yellow leaf. The fly struggles with all his might - and crawls slowly onto the leaf- a magnificent effort and ... gets away.

    And how would Leonardo handle this? He knew he had had a fly -- he felt the vibrations -- and spiders know how to "read" the vibrations. And now -- he knew he no longer had the fly. Was he disappointed? Was he upset with himself for not maintaining his web? Guess what he did next!

    Well --- the very next morning -- I checked his website -- it was cleaned up! It wasn't perfect - there were still bits and pieces of very tiny leaves scattered throughout the web -- but all the leaves - big, medium and small were gone -- Leonardo had done housekeeping!

    And -- what was his attitude toward his website now? While he was deep within his crack, working on his silk overcoat was he keeping a leg up -- so to speak --(i.e., touching a strand of silk from his web so he could feel changes in vibration)? Was he multitasking? Not too shabby for my little guy!

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  12. Really effective info, lots of thanks for the article.

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  13. Anon, what a great comment! Thanks so much for stopping by and relating that story. It will make smile all day. :-)

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  14. Clovis6:50 PM

    I too have observed the spiders and their ability to solve problems.
    I have an hypohesis here for comment. The insect brains are too small to do all the work. But how would it be if insects used a form of cloud computing to solve problems? Mobile phones can be linked to work together on tasks beyond their individual capability. So too can humans. So why not insects? If this is how it is done, then all we need to work out is how do they comunicate with each others brains. Looking in this direction who knows what we might learn about termites, bees, humans.

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  15. Anonymous10:05 PM

    Have you ever watched a flock of birds? How they move in synchrosy in terms of direction, speed, and even the rhythm of wing flapping and gliding motions?

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  16. Anonymous5:26 PM

    I will continue to anthropomorphize, I don't care what any ethnobiologist says. My little bathroom spider has an interior dialog going on.

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  17. Anonymous2:56 PM

    About ten years ago I noticed a very large handsome male orb web garden spider courting a very large female who was sitting in the centre of her web. One of the hawsers of the female's web was attached at an angle of about 40 degrees to one of a bunch of lavender twigs. The male had spun five parallel strands of web between the twig and the hawser, the longest was about 23mm and the shortest about 9mm they were evenly spaced at about 4mm apart. The male then sat back onto the remaining twigs and with his four front feet began to play (tunes) on the harp which he had constructed, His feet plucked the strings in rapid succession and each (tune) lasted about three of four seconds. Between each (tune) he waited for a response from the female. After four (tunes)she came down the hawser to investigate he then played one more (tune) and she tucked all her legs in, he then dived up to her checked that all her legs were properly tucked in and quickly mated with her, he then jumped of and absailed down to the ground and ran off.

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  18. Anonymous4:06 PM

    Hi, I'm the anonymous who saw the musical spider see above.
    In the 1980s there was a television programme called "take another look". In one episode it showed a spider intelligence test. The researchers set up special racks in a very large room with a soft board ceiling at about seven feet high. They then released 1000 orb web garden spiders who built their webs on the racks. The racks were then tilted a little bit, next the researchers hung cotton threads from the ceiling one into each web and introduced a slight breeze. The cotton threads wavered in the breeze which interfered with the operation of the webs. The researchers watched to see what the spiders would do. About 960 of them abandoned their webs, 36 cut a hole in their web to let the thread hang through which wasn't much good when the breezes was turned on. 6 of them attached a strand of web to the end of the cotton, climbed up the cotton to the ceiling, pulled the cotton thread up to the ceiling with the strand of web, stuck it to the ceiling with sticky web and absailed back down to their webs. The film showed one of them doing it. Spider IQ 167+.

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  19. Great comments! The amazing thing to me was that there was such variation in their behaviors. Thanks for visiting!

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