Building a web is a complicated business, involving an intricate series of inter-connected stages. How does a spider know what to do?
It doesn’t learn the pattern or ‘blueprint’ from previous examples, or from its parents.
Is the ‘knowledge’ inherited? I thought that only genes are inherited, and genes are codes for how to build the proteins that build the cells that build the creature. They don’t contain ‘blueprints’ for webs.
So… how?
The same way that birds know how to build nests, they just know
Why couldn’t they? They contain the information necessary not only to provoke the formation of body parts, but to arrange them into the right places, so why not, say, arranging neurons into the specific configuration necessary to provoke or enable a certain kind of behaviour or data processing.
Spiders’ ability to build webs is information, but so is the arrangement of stripes on a zebra.
According to some twin studies, they seem to also contain family names, mannerisms, and habits. Seems twins brought up in different homes end up marrying women with the same names or drinking their coffee exactly the same way or sharing many mannerisms that are peculiar to them. So if that can be inherited, then so can spiderweb-making.
If you think of it, how does any creature know anything? Why will pandas only eat eucalyptus? There’s a whole dang forest out there; nothing’s stopping them from munching down on any other leaf or tree or even chomping a snake but they don’t.
It would be amazing if spiders actually did learn to build webs. Seems that would be more amazing and require greater “brain power” than inherited interaction patters with the environment. Of course, birds that grow up not hearing their species sing, IIRC from some anicent PBS tv show, don’t sing “as well” as those that grow up hearing mom and dad, etc. So there’s an interaction.
<nitpick>Pandas eat bamboo; koalas eat eucalyptus.</nitpick>
I’m pretty sure those stories are false, or at least highly exaggerated.
I’m guessing it’s closer to “If you compare enough bits of information, eventually you will find some matches.” Kind of like reading Nostradamus. f you make enough vague predictions, eventually you can claim some of them are right.
‘They just know’ isn’t an answer.
The comparison with birds doesn’t help. Small birds usually have (a) the nest they grew up in and (b) other visible bird nests and (c) the behaviour of other birds (including senior generations) to provide cues and clues. A spider can be born, live and die without seeing another spider, or another web, and yet build webs perfectly successfully.
I guess the point here would be not whether or not genes could carry this kind of data, but whether or not they do. I have read about DNA and RNA and reverse transcriptase and so on, and from this I can see how the blueprint for an amino acid can be copied from parent to child. Personally, I haven’t come across any explanation concerning how such a thing as the complicated sequence of steps required to build a spider’s web could be passed on genetically, i.e. a process of coding and decoding, via known genetic mechanisms, that would enable this inheritance to work.
Apples and oranges. Stripes are physical structure. I know how information concerning the physical structure of the animal is stored and transmitted genetically. Building a web is a process that, at least from an anthropomorphic point of view (and this may be a classic error of thinking) seems to require knowledge or a ‘blueprint’. It requires certain tasks to be performed before other tasks. The early stages make no sense without the later stages, and vice-versa. It also calls for tasks to be completed with respect to spatial orientation on a scale vastly greater than the animal itself. I don’t know how this information or this ability can be coded and decoded genetically.
Possibly, but the ones I’m thinking of (and Quiddity Glomfuster appears to be referring to) go along the lines of "twin boys adopted by different families were both named Bert (by their adoptive parents) and both grew up to be insurance salesmen; they both hated dogs, loved spicy food, both married women called bernadette, but both divorced after three years and remarried, both to women named Lucinda, who bore them two sons which both couples named Harry and Binky. They were unaware of each others’ existence until the day when they were involved in a head-on collision (their cars were identical make, model, colour and year) - they had both been intending to drive to the other’s home town!
AFAIK, these stories don’t have any reality outside of the pages of Reader’s Digest.
IANA spider guy but innate behaviors are pretty common.
http://www.cals.ncsu.edu/course/ent425/tutorial/Behavior/index.html
Googling the subject produces a range of views, but there is a lot more than anecdotal evidence that identical twins raised separately share many traits. Here’s a link
Not really; it’s all encoded genetically. What we’re talking about here is instinct - admittedly, quite organised, complex instinct in the case of spider webs, but once you concede that simple instinct (such as specific responses to a given stimulus) can be encoded and transmitted genetically, it should be no problem to conceive of more complex behaviours being able to being built in the same way.
Spider web-building behavior, like most other behavior of arthopods and most other invertebrates, is innate and hard-wired. Each species has their characteristic behaviors that results in the web typical of that species. Spiders do not learn this from their parents or any other spiders.
How exactly this happens is one of the great mysteries of biology. We do know that many behaviors are genetic; crosses between individuals from species or populations with different behaviors can result in offspring with intermediate behaviors. We don’t at this point have a good idea of how this happens.
Some bird behavior is learned, and some is innate. In general, nest-building behavior in birds is innate. A bird will build its species specific nest without ever having been taught to do so. In some birds, the song is innate; in others it must be learned from a parent.
We know they do; we just don’t know how. And you know almost as much about the mechanism as scientists do. 
I would find this the least suprising aspect - I can easily see how certain individuals have brains pre-wired to accept the notion of a deity, much more than a preference for girls named Susan.
I’m still suspicious about these studies - there does seem to be a large element of confirmation bias involved.
Well, they know not to use FrontPage … 
They Have read the FM.
Thank you, Colibri, for this very clear reply.
I agree with you that it seems a difficult question to answer. I also happen to think that web-building is a particularly taxing instance of what is referred to (both casually and in precise scientific contexts) as ‘instinctive’ behaviour. I think I’m fascinated by how much we know, or don’t know, about the mechanisms which enable these ‘instinctive’ beahviours to be passed on genetically. I only completed high-school level biology, but I’ve met a few zoologists since and I have learned a little bit more here and there, and I still haven’t come across a satisfying explanation (or maybe such an explanation would lie beyond my level of comprehension).
If you don’t accept it as simple instinct, encoded and passed on as genes, I’m not sure what else there is to suggest instead. Magic?
True there might be something else beyond “genes”, but outside of telepathic beams connecting the spider race, it’s still got to come down to something passed on through a similar process as passing on genes. The only other suggestion I would have would be “trial and error”, but I’m not sure spiders live long enough for that.
One conceptual problem you might be having is the idea of a “blueprint”. It is highly unlikely that spiders have an innate blueprint for building a web, or birds have an innate blueprint for building a nest.
They don’t have a blueprint, they have a “recipe”. A set of stereotyped behaviors that, in the right environment, will result in a nest or web of a certain type being built. The spider doesn’t have a concept of a finished web in its mind when it is building the web. Rather it has a certain set of instructions…perhaps something like:
Of course, how these “steps” are entered into the spider’s firmware nervous system is unknown, but we can observe the methods animals use to construct structures. And they might use completely different rules for web building than I outlined above, but slight changes in the rules could result in very different finished webs, and very different starting evironments could do the same.
For another example, beaver dams. A beaver doesn’t have a plan of a finished dam, it has a simple rule…when you hear running water, add more sticks and mud. Any time the dam starts to leak, the beaver hears the water trickle and gets the feeling it should pile more sticks on the dam. But if you play a tape recording of trickling water, the beavers will keep adding sticks until the dam is enourmously overbuilt. And of course, we still don’t know on a physical or neurological level how or why the sound of trickling water makes a beaver want to cut down a tree and pile up the sticks, but it’s a lot easier to imagine how this behavior could evolve from simpler behavior. Likely the ancestors of dam-building beavers built lodges out of sticks, and the sound of trickling water meant their home was leaking, and time to reinforce it. And a slight change in this behavior lead to the creation of dams.
So if you think “recipe”, or a set of behavoirs that act together to create a structure, rather than “blueprint”, animal construction behavior won’t seem so baffling. Not that it’s explained, exactly, but just that the behavior doesn’t come out of nowhere.