Yona (FS): Majority of yaks are arachnophobic?
DM: Well, afraid of just about any tiny, swarming, creepy-crawly creature, but spiders are the most effective. Like you were saying: Smash one, and twelve more crawl up your leg.
Ocellus (TS): I don't know if spiders "swarm" all that often…
Sandbar (AJ): They do in D&D.
Ocellus (TS): Oh, yeah, good point.
DM: I take it you're playing Yona as unafraid, though?
Yona (FS): I suppose… Yona is already unlike a lot of her people for traveling outside her home country, wanting to learn how to make friends. That is already scary enough. So what are a few spiders?
Smolder (RT): Awww…!
Silverstream (PP): What a sweet, helpful-in-this-situation backstory!
DM: Just as well. They'd be more terrified of you yelling and stomping than you would be of them anyway!
Gallus (RD): …That would turn the swarm hostile, wouldn't it.
DM: Maaaaaaybe. It IS a trap for yaks. But instead, they offer to help Yona escape the maze and find her friends!
Yona (FS): Um, I'm not playing Fluttershy right now, how would they–
DM: These are spiders who have been living in the branches of a magical tree. Of course they can communicate. You're lucky they don't sing and dance.
I always assumed that just about all spiders are solitary, but a bit of Googling suggests that some spiders do have social tendencies and can form colonies numbered in the hundreds. Fun fun fun!
"They'd go hostile if we went murder-hobo, wouldn't they?" "Maaaaybe."
Storytime, tell about a time you created this situation as a GM, or encountered it as a player. A time when being hostile would have been the equivalent of committing self-TPK.
I was in a HALF Party Kill in my early RP days.
We had the standard group; a wizard, a ranger, a thief and my run-away gladiator (fighter) character.
I forget the details, but we were consulting with the ruler of a city-state when for some reason, the wizard didn't like his attitude and decided to do "something" about it.
What he had forgotten was that there was a squad of the Duke's bodyguards in the chamber, fully armed and armored. The DM had described them in a way that made them seem as just set dressing, but now they were moving in. That wasn't all. The Duke had been toying with a dagger that turned out to be MAGIC and knocked the wizard on his ass!
The thief wasn't going to let some "one percenter" get away with that and attacked.
The ranger had more sense and dove out a window with me close behind because I had screwed up making my character, giving him good skills, but low scores in STR and HP (That's why he ran away, he would have died as a gladiator).
Sooo... half the party killed, the other half on the run for "conspiracy to commit murder".
I had an NPC like that in a game I ran a few years ago. He wasn't actually indestructible, but he was an Epic Wizard compared to a level 5 party. Of course, I'd MET players before, so if they decided to attack I had a plan in place where if they impressed him enough then he'd still help them. Any crit or max damage spell genre the party a 5% chance, and the wizard took it easy on them since he wasn't in any real danger.
They did manage to survive the fight. Then when they were given the option to teleport out, the teleport spell went wonky because someone had pilfered an item with time magic from within the tower and the whole party wound up teleporting 500 years into the past.
I've thrown an indestructible NPC at my party before. Well, not actually indestructible, just a high level spellcaster that spent all their top level slots on defensive spells such that it would be impractical to make them run out of hit points.
Because they were AWARE of their own nigh-immortality, I just had them no-sell the party's Sudden Yet Inevitable Assault until they got the gorram idea, had them dispense the quest token, then departed in a giant fireball that left everybody at death's door because they were violent jerks. :)
We encountered almost this EXACT situation in the last game we played. Swarm of spiders, one of our guys noticed that they didn't immediately attack and tried talking to them, ended up being able to communicate and was told that we were the first who didn't try to attack them so they were going to let us live.
I, on the other hand, was just waiting for our commander to do much as twitch his nose and I was going to Fireball the hell out of everything that wasn't resistant or immune to fire damage. Then do it again with an energy substitution just to make sure. ;)
I've seen spiders get very social in my boiler room. They had a dense sheet of web spanning the entire room about a foot below the ceiling, and spiders just hanging out all throughout it.
I tolerate a few spiders in my house to kill off the other insects, but if they were to unionize, I'd have to break out the spray can and flip-flops because I do have an arachnophobe living in my household and what she doesn't know won't cause her to yell murder. XD
What would they unionize for? More flies? Time off to tend to their kids? (If that's a per-child thing, swarms mean the parental benefits add up fast.)
None yet, but I am planning to run a game... It's going to be my fourth try, and I've already decided it's not going to be the most serious of attempts. *pulls out a notebook*
On the one side, a military-esque gang that had taken over a city.
On the other, a street gang of ninja from the surrounding countryside.
The party is between them as they encounter each other, weapons getting ready. Party looks for any way out of the crossfire, but this is on a street with no side alleys, and all nearby buildings are locked up tight: the residents don't want any part of this.
And then the two opposing forces begin a dance-off, with rap-battle-style songs.
Turns out, neither one really wants to be there, but each side is under orders from up above. So they get into a dance contest, and (once the party figures out what's going on and get involved) subtly arrange for the PCs to win as a third party, giving both sides excuse to leave without tipping off their superiors.
Harvestmen are the ones really known for swarming. They're also non-venomous, which would explain the last page. (Just to clarify, they're closely related to spiders and often confused for them, but they're not spiders. You can tell since they don't have cleanly divided body segments.)
For arachnophobes...might I suggest Adrian Tchaikovsky's excellent novel "Children of Time"? It really changed how I look at spiders. Just, ya know, be warned that there are spiders in it.