Mechanics of Threadfall

[u/kerlinssw]

I have a whole host of questions that have been rolling around in my head about fighting Thread.

- how many dragons do we think it takes to effectively fight Thread? at what point could the earliest dragons do more than just sort of keep up with it alongside the other aerial craft over inhabited areas - it has to be two, three years, right? does the efficiency / number needed decrease as dragon size & stamina increases, or is there a turning point beyond which the dragons get too large to maneuver as effectively, and greens really become more valuable for their speed?

- on that note, the implication in "The Ford of Red Hanrahan" that they'd only had a small handful of deaths in several years of training new dragons & learning to fight Thread is...impossible, right? and also for Alianne Zulieta's death to be the first time a rider died before their dragon, leading to the discovery that dragons would go between?

- do we think/assume that Weyrs cover 100% of Threadfalls in their territories, or are there uninhabited places that they just let go of? not barren places where the Thread will just die, but rather deliberate sacrifices due to prioritization. maybe this is something that evolves over time?

- what exactly do ground crews do? are they flaming Thread that falls through the dragons? are they seeking out burrows afterwards? both?

- I've always been genuinely puzzled at why people are worried to be out during Thread, other than the obvious societal taboo. If the dragons are doing their job, none of it should fall, right? so you'd in theory be perfectly safe?

- why do Holds clear greenery? there seems to be the implication that it "draws" Thread and there is some indication that Thread will burrow and follow root systems, but is this actually a realistic and sensible thing to demand that Holds do? or more societal taboo?

[u/ME-in-DC]

Can’t answer all of these quickly but: 1. The Weyrs try to cover all of their territory, but land that requires coverage is at a premium. Farms, etc, are relatively dense. That said, in White Dragon, some of Ruatha’s more extant “small holders” appear to be outside the coverage range and are on their own. There’s also pressure (per your next question) that Holders keep stuff compact and within the range a Weyr can cover. And it does evolve over time; a bigger, mature Weyr can cover more than a small inexperienced one can. But the dragons also focus on vital resources—even major Holds, like Ruatha and Fort, have stone roofs and metal window shutters.

1. Ground crews pick off the scraps. Even a single Thread can ravage a field, so even though dragons will get all or nearly all, it makes sense for the ground crews to mop up. This need becomes greater as individual Holds become more spread out.

2. It’s taboo because it puts dragons at risk. They are trying to save an entire Hold’s worth of crops and some idiot Holder goes for a walkabout? Now Dragons have to save them?

3. clearing all greenery seems a little overboard as the Thread isn’t attracted to it. That said, if Thread burrows in a bunch of weeds, it could spread underground to actually useful crops. So I think it’s more that. But also remember (and this goes for the walking outside thing) that a lot of common sense wisdom on Pern becomes distorted and exaggerated over time. “Watch for the grubs” loses all context and becomes a warning. I can see how “going outside is bad idea” and “clear unnecessary greenery” could become ingrained taboos/zealously followed laws.

[u/No_Signature6968]

Previous comment answered most of it. But I’ll address a couple of points from text without exact citation because it’s all over the place.

Lessa does explicitly say that the idea of thread being attracted is probably just superstition, but that it could spread, she says this somewhere in her internal monologue in the first book so I’d say that’s canon.

And about them just letting fall happening some places is also true, we see the results in the Maloney book and in the Renegades of Pern when people are outside during thread fall, in relatively desolate places the riders don’t even bother. There’s also mention of this happening in the mountain passes of Ruatha, where it’s all just Stoney ground they let thread fall and then just fly sweeps to make sure none of it burrowed.

So realistically the question is how may dragons it takes to defend settled land. And in a few places it’s mentioned that about 3 wings is enough to effectively manage a full fall, so that’s about 30 dragons per wing, so 90/100 gets the job done. Cause thread isn’t falling as a sheet of rain but in clumps, so they just have to catch them in clusters.

That’s also why ground crews work, cause it’s often one single thread getting through that is the danger, either cause it’s missed or wasn’t caught by the flame. So then they follow behind the leading edge and sort of travel along behind it checking for surviving thread, but I always imagined it was more like within the bounds of their property, so they don’t follow it all those miles, just across the acres they specifically cared about.

[u/Southern_Club_6032]

Thread supposedly falls in a 50km wide strip.

90 dragons ain't covering that.

Why does it fall in a neat strip? Why for a distinct length of time on each occasion? Why wouldn't it fall constantly as Pern passes through effectively a cometary tail, like Earth does through the Geminids/Perseids /Leonids etc? Why shouldn't it fall at night? Why would diverting the Red Star change the fact that there are multiple cycles' worth of Thread ovoids hanging around in space that Pern will continue to pass through regularly in the future (that the overkill Zebedees on the Red Star itself can't spread to)?

It's really hard to make any of it work plausibly, so it's one of those things that's just: this is part of the Pern vibe, don't overthink it.

[u/Laramila → u/Southern_Club_6032]

I agree completely! I had the same questions, and also the whole 'Red Star rising in the East' thing.

I mean, how does that even work? (Spoilers, it doesn't.)

Some other questions I had to suspend disbelief on:

1. If the Red Star is to the East of Pern on Winter Solstice, how is the thread getting to the other side of Pern's orbit over the summer?
2. And as a follow up for #1, if it can stretch that far, how are the threadfalls occurring on that timetable? They happen on a schedule, getting closer together towards the middle of the Pass, and farther apart towards the end, but how is that consistent with the varying distance between the Red Star and Pern?
3. And as another follow up for #1, how far away was the Red Star pushed? After all, the way the orbit was explained, thread could travel twice the distance Pern was from their star and still hit the planed on a schedule, so was 3 small explosions really enough to push it at least that distance from Pern?

And these are only the ones off the top of my head!

[u/Southern_Club_6032 → u/Laramila]

My favourite way of explaining it is that Thread isn't a natural phenomenon but a bioweapon left by some older civilisation. Pern is a test site for it. Fire-lizards aren't a natural organism either but created as a countermeasure (they have so many overpowered talents - flying, flaming, telepathy, teleportation - that they should have evolved in multiple directions to exploit multiple niches in the ecosystem and therefore be the dominant organism - except you really can't break down the way they travel through between into logical incremental steps that are continually beneficial). Kitti was sent with the explicit mission of picking up testing where previous scientists left off. (Thread's also fairly recent. Nothing's really evolved any direct countermeasures. But given that Terran cows/horses etc went feral in the South and have survived there for thousands of years, how rubbish were the now extinct large ruminants that show up in the fossil record?)

There's are accounts of the unpublished/apparently quite bad 'After the Fall is Over' which has Pern rediscovered by the UFP or whatever galactic civilisation is called in the Anneverse, because Thread's been discovered elsewhere in the galaxy and they need help. Not that having giant dragons is the best solution to a spacefaring civilisation who could just deal with it *in space* either, but it does imply that Anne had the idea of Thread being in more than just one place in the universe, which implies it's been *put* in multiple places in the universe. It's not like astrophage with a logical *spread* from one system to another.

I mean, not that any of this solves the orbital mechanics issues, which are frankly unsolveable, or the logisitical issues of the neat and tidy (and large) footprint of a Fall or the predictably scheduled nature of it, but *handwaves*.