Wisdom of the spider

The mornings have been cool and misty this week and I have noticed webs on the fence wires on more than one occasion. Within an hour or so the dew evaporates as the air warms. The breeze hastens and this dismantles the laborious work of the night before. I like the image below. I like the way in which the dark parts of each dew droplet are highlighted in the upper half of the photo and how the light parts of each droplet are highlighted in the lower part of the photo. I like the way in which the inner-most hub looks like a densely populated solar map, complete with sun and with six planetary objects and their associated moons. The business of constructing a web such as this is a fascinating one. It involves the formation of a simple infrastructure comprised of drop lines, a perimeter, and a series of spokes which radiate from the center. Once these elements are established the spider spins an auxiliary spiral of non-sticky threads from the inner hub to the perimeter of the web. The animal then turns and deposits a sticky, capture spiral, using the auxiliary spiral as scaffolding along which to negotiate the web and as a guide. Once the web is finished the spider travels about by moving along the radial threads and traversing the auxiliary spiral. Unwary prey are caught by the sticky elements of the capture spiral. As I thought about the cognitive power needed to carry out this sort of construction I wondered about the size and complexity of the brain of a spider. I was surprised to learn that, for their size, spiders have some of the largest brains of any organism we know. Workers at the Universidad de Costa Rica and at the Smithsonian Tropical Research Institute showed that the central nervous system of the smallest spiders occupy nearly 80% of their total body space, including 25% of the volume of the legs. They suspect that very little spiders might be mostly brain. Hallerโ€™s rule predicts that as body size goes down, the proportion of the body taken up by the brain increases. Human brains represent just 2-3% of body mass. The brains of some of the tiniest ants represent nearly 15% of their biomass, and some very small spiders are much smaller than ants. [The preceding facts were taken from a 2011 issue of Smithsonian Science.] Something called an encephalization quotient measures the ratio between actual brain mass and that predicted for an animal of a given size; it is thought by some to reflect cognitive ability or intelligence. By this measure, the Jumping Spider is recognized as having the highest EQ among invertebrate animals. Consider, for a moment, that the reason we are quick to marvel at the ability of a spider to create such a structure as intricate as a web is because we can’t imagine doing it ourselves, on whatever scale, within an hour, and at least once each day. Let alone creating the silk with which to build the construction, let alone determining whether a leaf or a tiny insect, or a dangerous wasp or a preferred prey item has encountered the web by sensing the vibrations which travel the signal line to highly sensitive legs. Marvel at that for a moment and then consider where you’d like to place the spider along the entirely fictitious Great Chain of Being!

24 thoughts on “Wisdom of the spider

  1. I’ve skimmed the comments as I’ve scrolled down to where I can write my own comment. I am intrigued by your point directly above, the response to Steve. I have a very long post in draft right now, on market writing, and as I’ve worked on it I can’t escape the feeling that we humans are very deeply tied to “the pressures of natural selection.” I think our so-called social and cultural evolution merely masks our more deeply buried human instincts, and this lack of awareness is to our detriment.

    I also wanted to mention that I appreciate the infusion of humility in the post, and the image is arresting.

    • Ah … the topic of human evolution. One of the most common questions that students ask me concerns current patterns of human evolution. I think you’ve cut-to-the-chase nicely when you suggest that social and cultural change have occupied our human stage for several hundred thousand years. I’m guessing that the forces of natural selection haven’t been ‘felt’ by our species for longer than that. What the future holds for our species, I cannot say. I have observed, however, that most of the difficulties that we have gotten ourselves into over the last several centuries do not reflect well on Homo sapiens as a species. Perhaps, in the long run, we will, in the ‘eyes’ of natural selection, be deemed unfit or maladapted. If that is the case, we will simply go extinct … just like that! Poof. D

      • I just reread my comment to be sure I wasn’t repeating myself here as I have remarked on this before elsewhere, I guess. When you look at the planet, it is my opinion that we are to the Earth what the appendix is to our bodies. Unnecessary to the ecological system that keeps itself in balance, we create, rather than collect but the result is the same, poisons that could kill the organisms that make up the life of the planet. So, yes…poof. Someday the appendix gets extracted and the earthly body recovers and flourishes. It does not need our consciousness to recognize its flourishing.

        • Sad to say that the planet would perhaps be better off without us. But, our rise has been as natural as the rise of any other species. It’s just that our species doesn’t follow the rules anymore and as such, we’ve created difficulties which are, I believe at this point, irreversible. So our very unusual, and highly out-sized brain, has allowed us to build computers and cure disease … but, ultimately I believe, it will be our downfall. Now, how depressing a thought is that? D

  2. Great image – it’s interesting to see that the droplets at intersections are typically larger than the others … which adds a subtle second layer of regularity. As you praise the spider I can’t help thinking about Spider Man – no wonder a spider can be a super hero. Is there a larger (perhaps non-insect) animal that can produce similar structures? If not, is there a simple explanation why this would not “scale”?

    • Surely mass would be an issue. I’m not sure what the weight of your average spider is, but I’m certain it’s quite small. Any larger vertebrate like a mouse or a shrew would be too massive to be supported by such delicate structures. Now .. if they were to find some way of producing multi-ply silk then, perhaps, mouse-webs might be a possibility! Certain bird’s nests would be the obvious, serious, answer … but even loosely arranged nests, high in the trees, can’t compare to the intricacy of construction of a spider’s web. Unique, I’d say, among the animals. D

      • Thanks – I just wondered if it would be possible to scale anything – including the threads … which would rather be ‘ropes’ for bigger animals … but I guess I have seen too many movies ๐Ÿ™‚

        • Funny you should mention the movies. J and I just finished watching the Lord of the Rings on DVD. In the Return of the King, when Frodo gets caught in Shelob’s web (Shelob, you will recall, is a mammoth spider), I was especially careful to take a look to see if the silk fibers scaled properly. They seemed to and were able to hold Frodo suspended. I’m not sure how much a Hobbit weighs but I’d say that the web was capable of holding 50 – 75 pounds. Pretty good huh? Too bad it’s just make-pretend! D

  3. What I find amazing is the immense span of time required for enough happy coincidences to occur in order for that pattern of behaviour and attendant body functions to emerge. So, for the moment, one supposes spiders are well adapted to their environment and to their food. But what’s the next logical change I wonder? Will mankind be around long enough for a few mutations to occur that make the spiders better suited for function around man made structures? Hard to say. For now, of course, doorways, bridges, clotheslines, flagpoles and such serve as suitable treelike structures and maybe that will be enough; no further mutations will provide an advantage. Besides our time is just measured in the centuries and I imagine those changes required, step-by-step changes that spanned millions of years. Nonetheless it’s a lovely crisp fall morning here. No wind and 2 C. There’s a spider web stretching between my shed and the clothesline. It, too, carries some dew.

    • I should not reveal my snobbish, professorial, nature by saying that I am impressed with the precision with which you clearly understand Darwin’s recipe. Some of my students graduate still having not quite grasped it. The randomness of mutation and the nonrandom (though fortuitous) fit between mutation and environmental challenge. Your phrase ‘happy coincidence’ is right on … and is, truth be told, perhaps the primary obstacle many folks have with Natural Selection. They say, ‘It’s just so random. How can this world have developed from random processes?’ Mutation is random, but the fit between chance mutation and environmental challenge is anything but. A+

  4. It’s a truly stunning shot David … the dew drops perfectly halved spheres of dark and light. As for the spider I’m not surprised to read that so much of its body is brain. They are very clever creatures defying gravity with their threads and lines … and we currently have an invasion. It’s been a good year for spiders here in Scotland and they are marching in droves into the house as the nights cool ๐Ÿ™‚

  5. This image reminds me of Halloween in the black/white. Spiders creep me out no matter how amazing their webs are. And they ARE amazing.

    • Would it creep you out to know that your sister-in-law has befriended a number of very large wolf spiders that live in the house? There’s the one in the upstairs bathroom … the one in the back hall … and, oh yes, there’s the one in the kitchen … not to mention the large cohort in the basement. She greets them like old friends each time they appear and tells them to ‘watch out for the kitties.’ She says it’s an artist’s thing … you know, they weave, she weaves, so she can relate to them … on some level. She just remarked, ‘I do vacuum them from the ceilings, you know.’

      • Are you kidding me? Take a picture. I can only image how hideous and frightening a wolf spider is! Aren’t you afraid they will crawl into your bed at night? I have dispatched one each night since the weather has turned colder. This variety is a kind of pale whitish/yellow. Ugh.

        • The wolf spiders tend to like moist areas … so we find them in the bathroom and basement mostly. I think the bed wouldn’t be to their liking! One does have to watch our for spiders however, some bites can be very, very, nasty and dangerous indeed. D

  6. Some may say that spiders, and other amazing organisms, are just acting out of some genetic messaging and not really aware of what they are doing. Bah to them! I really do think that at times, or most of the time, humans are at a distinct disadvantage because of our lack, well many of us, of humility. Our brains have obviously helped us in many ways, and who knows what the future holds, but in many other ways we are at a loss for much of what is required for survival. We can’t fight a lick, our dietary needs are pitifully complicated, and our energy level can’t compare with those who forage for their sustenance all day long. And our biggest disadvantage, which for the most part comes totally from our mental weakness, is desire … for sweets, for relaxation, for entertainment and so on. Of course, this is all just my opinion. But why would I express anyone else’s? ๐Ÿ™‚ I got all wound up and forget to comment on the image … it happens all too often. I like web shots and this is a nice one, David. The reversal of tones is a nice effect that I think is similar to that of the ground glass in a view camera.

    • I would agree with you on both counts Steve. I too cannot believe that what nonhuman organisms do is entirely hard wired and instinctive. All one has to do is to watch a spider construct its web and you can tell that it’s making decisions. It’s not simply a matter of pushing the start button and the thing then goes through a series of prescribed movements. Much to the contrary. To my eye there’s lots of cognitive processing involved. The spider comes up against something out-of-the-ordinary and is able to adapt its behavior to account, to adjust. So, yes, you and I are in the same camp there. Now, having said that, there are certainly many other behaviors which are hard-wired … such as many instinctive behaviors that all animals display. Your other point is a good one as well. Some have viewed humans as having gone beyond feeling the pressures of natural selection. Some would say that social and cultural evolution are now moving us in the directions you point out. We seem to be moving away from the maintenance of skills that got us here in the first place … our myriad abilities to use our out-sized brains to compete. Perhaps these shifts may, ultimately, be judged (by nature) to be maladaptive … and perhaps this will be our ultimate downfall? Now, there’s a depressing thought. D

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