Made a forum account just for this post, cause it seems important.
Until just now it was my understanding that a trained Giant Cave Spider doesn't shoot webs at hostiles, that's what the wiki says and I'm only playing my second proper fortress, so I pretty much rely on the wiki for everything, so I'm gonna go ahead and assume my GCS based execution chamber filling literally every tile with silk the first time I used it is unusual, I'll go over what I did in as much detail as possible, to the point where it's probably unnecessary, because I am but a Dabbling Fortress Builder and Not Scientist, though I do plan on posting on this thread again for my next test(s), where I'll try removing certain steps to find out which ones are and aren't necessary. Also I am currently using 0.44.05, I've not updated yet cause I'm waiting for the inevitable fall of the fortress, I'm surprised I've even lasted this long.
So, first possible important detail: The 5 GCSs are pastured in a 7x7 room, at the end of a 20 tile long, 1 tile wide hallway completely filled with cage traps on a subterranean soil layer 3 z-levels from the surface, this room was initially a precaution to prevent a GCS from reverting to wild and eating my fortress' entire population, later used as a mating room to build up my trained GCS numbers just cause it was already made and not being used for much else now that my trainers are somewhat competent, and following my most recent goblin siege I decided I was going to feed the prisoners to the GCSs cause my military is already pretty well trained and pitting them against 2 goblins and 2 beak dogs seemed like more effort than it was worth, and also I thought it would be mildly amusing, their cages were built 1 tile's distance diagonally away from the 4 corners of the room, inside the pasture, beak dogs on the bottom, goblin hammerman on the top left, goblin spearman top right.
Possibly related detail #2: I caught the goblins on a different IRL day to building the cages and releasing them via lever, I hope that didn't have any effect on things but it's a possibility.
3rd possible relevant detail: I forgot to unforbid the goblins' equipment before designating dumping, they still had arms and armour when put in with the GCSs (didn't help them at all, and the helms probably boosted web production), and I am aware that during sieges any trained GCS will not web invaders, but maybe they react differently when there isn't an ongoing siege?
Next year's siege I'll do as many tests as my military will allow me to gather subjects for, hopefully providing me with at least 1 beak dog and 1 troll for testing on intelligence levels, and I might try to get an elf or two, I'm not at war with them (yet) but they are an important test subject for this; their unique relationship with wildlife could mean that the hippies are even more useless than I thought they are an unsuitable medium for generating silk.
Priority of tests will be as follows:
1)Test if exiting the game/turning off computer is necessary
2)Test if subject needs to be in GCS pasture
3)Test if subject must be armed during procedure
4)Test if subject must be armoured during procedure
5)Test if subject may be restrained
After the first 4 tests I should be able to determine what exactly caused the GCSs to shoot webs when usually they wouldn't, unless of course all tests turn out to prove their potentially relevant detail to actually be irrelevant.
Bonus: If tests 2 gives results that allow for it, use of fortifications could mean only one subject is needed, or perhaps for greater efficiency, one subject per GCS, however in order to actually collect the webs a marksdwarf may be needed to clear the area before any doors are unlocked, though info from test 5 may make this less of an issue
I had 3 other theories on this: that the GCSs being descended from male and female Hist Fig GCSs that I captured had some effect on things, that the GCSs being pregnant was somehow relevant, or that they are young enough to have not had to receive training yet did something, all of which were debunked when I checked the combat logs, as luck would have it I had unintentionally included control groups, there is a single male present and one of the females has recently been caught from the wild and thus was neither untrained nor a Hist Fig or descendent of, that meant if any of these were true, one of the GCSs would have no "the giant cave spider shoots out thick strands of webbing" in it's combat log, but all GCSs shot webs.
Anyone willing to test this out in 0.44.06 please do, I'm going to be converting the fortress of Bronzevipers into a GCS lab for the next 1-5 years depending on how many goblins my military kills before they have the chance to get caged per siege, so I won't be updating anytime soon. Also if anyone comes up with results before me please share, even if it is that you were able to replicate the results under the exact same conditions, it's at least proof that my game hasn't bugged out or something.
I've saved a screenshot of the silky room (been mostly harvested cause I accidentally left the game running before thinking to take the screenshot) while showing that the GCSs are tame with v (and also a potter busy harvesting silk), and I also got a screenshot of the combat log showing a goblin being webbed then bitten and repeatedly shaken around, will post as evidence if someone tells me how, I don't really know how to forum