how many are in the swarm? and how do I calculate damage?

Treat the whole swarm as a single creature.

This almost just wiped out my Level 1 Party.

WTF?

Quote from Wechselschrat >>

This almost just wiped out my Level 1 Party.

WTF?

 Because it is a CR 1 creature.

Could a druid turn into this, it being a swarm an all?

Wouldn't it be 28 Quippers per Swarm, since one Quipper has 1hp.

I put one of these inside of a water elemental. It made for some pretty great times.

Hard to say, because standard quippers also deal 1 damage and the swarm deals 14. You could say that the swarm has 14 and the 28 hit points represents the fact that they're hard to hit and can kind of provide each other some form of cover. Personally I would agree that there are 28 and the 14 damage is due to the fact that not all of the swarm manages to get a bite in. Up to you though.

I love monsters that work off each other like this. I will be stealing this idea. In return I offer the following. An iron golem that has a fire elemental hiding inside allowing it to gain a free heal every round because of the fire damage. 

Quote from Legendary_Resist_Dance >>

I love monsters that work off each other like this. I will be stealing this idea. In return I offer the following. An iron golem that has a fire elemental hiding inside allowing it to gain a free heal every round because of the fire damage. 

 Evil. 

I love it. 

They have hit points, so you take off the damage taken.

So I was just dinking around with a cr1 merfolk guard or "deep guardian" that has a poisoned hand crossbow, and I was looking at cr 1 monsters for balance reference. Of course I see these and wonder how they'd stack up, initially I think the guardian can't hurt these effectively and would get straight shredded (and it would) but it did occur to me that their hand crossbows would be more effective than their spears because of the poison damage, even though logically the bolt isn't going to poison multiple fish (unless it spreads through water in which case they'd be unsafe to carry around underwater). It just raises an interesting question on whether swarms should have resistance to poison damage inflicted by a weapon. Although a poisoned longsword could sweep and nick multiple guys, so where do you draw the line at that point.

logically it should be the number of hit points the swarm has as the normal quipper has 1 hp

can i use this in  a swamp setting...like a variant of this?

Quote from SlyGallant >>

I put one of these inside of a water elemental. It made for some pretty great times.

 Borrowing this!

Oh no

It seems like there should be some kind of damage multipler for AOE. If the swarm succeeds a dex save against a fireball that normally would do 30 damage, the fireball does 15 damage to the swarm. But fireball does damage to everything in the range, so it feels like each individual quipper in the swarm should take that 15 and get obliterated. Thoughts on a homebrew rule? Or just leave as is?

.

My brother is planning on running call of the nether deep someday, and I’m thinking of making an action-oriented version of this for the 1st dungeon to suggest 2 him.

Swarm of ruidum-infected quippers
medium swarm of tiny beasts, unaligned solo
armour class 13 or 16 (see villain actions)
hit points: 28 (8d8-8)
speed 0ft, swim 40ft
str 13 (+1), dex 16 (+3), con 9 (-1), int 1 (-5), wis 7 (-2), cha 2 (-4)
saving throws: intelligence -3, wisdom +0, charisma -2. (See hive mind)
condition immunities: charmed, frightened, paralysed, grappled, petrified, prone, restrained, stunned.
senses: darkvision 60ft, passive perception 8
languages: none.
challenge 1 (200XP). PB+2
swarm: the swarm can occupy another creatures face and vice versa, the swarm can move through any opening large enough for a tiny quipper.
the swarm cannot regain hit points or gain temporary hit points and if it fails a saving throw against a damaging AOE it takes 7 (2d6) extra damage.
hive mind: the swarm losses its saving throw proficiencies when it has 14 hit points or below.
water breathing: the swarm can breathe only water.
actions
bite: melee weapon attack, +5 to hit or +8 after blood frenzy, reach 0ft, 1 target in the swarms space, hit: 10 (2d6+3) piercing damage or 6 (1d6+3) piercing damage if the swarm has 14 hit points or less.
bonus action
Blood frenzy: the swarm moves up to 1/2 its speed without AoO straight towards a creature below their hit point maximum and gains +3 to the next attack roll it makes against them before the end of the turn if it moved at least 20ft.
reactions
Share agony: when the swarm takes damage it can force a creature in its space to make a dc9 wisdom save, taking 3 (1d6) psychic damage on a failed save if the swarm has 15 hit points or higher or 2 (1d4) damage if the swarm has 14 hit points or less.
villain actions
the swarm can take a villain action at the end of another creatures turn or use a villain event at count 20 in initative.
it can only use 1 action/event per round and each only once per encounter.
round 1: malevolent pulsing(event): the swarm begins to pulse malevolently, its minds screaming in pain, when it next uses share agony before the end of the round the save is automatically failed and the creature takes an extra dice of damage.
round 2: feed and grow beyond all sight: the swarm becomes invisible but is surrounded by a veins-like network of red crystal around them, gaining a +4 bonus to AC until it takes damage.
round 3; revenge of the fallen: the swarm moves up to its speed without AoO and makes a melee weapon attack at +5 to hit with advantage, dealing 10 damage on a hit.
this cannot be used unless the swarm has 14 hit points or less.