Eureka Seven has the Skub Coral Antibodies which spawn when the command center is attacked by the big bad's oribiting laser cannons. They don't seem particularly intelligent but can cause massive amounts of casualties.
Similar to the paranoid schizophrenics example in Truth in Television below, Rena Ryuguu hasn't, as it is all a delusion caused by the Syndrome, maggots in her veins during the Atonement Arc. This leads her to claw at her wrists and neck - and she won't stop until they're all gone. She also had this problem when she contracted Hinamizawa Syndrome in Ibaraki, before the story even started, meaning she's had this happen at least once in every arc. And while we only see a few at a time during the main part of the arc, Rena's earlier description/flashback of the first time shows them literallyflowing out.
Shino Abarame from Naruto is an example similar to the Lutecia one above. His (and most, if not all of his clan's for that matter) abilities consist of manipulating a swarm of chakra-eating parasitic insects that he houses within his own body. Needless to say, it's never pretty when they find their next meal.
Swarm, the Nazi Made Of Bees, appeared once as a vast supercolony and was promptly taken out by the Thunderbolts.
This is essentially how Ultimate Galactus works, though scale is a bit off as every member of the swarm is the size of Taipei 101 and their victim is an entire planet.
The Flea from PS238 has the power to control insects, and he's used this as an offensive weapon on several occasions.
The page quote comes from Nicholas Cage's character in The Wicker Man, where Edward is subject to the bee mask by the villagers.
In The Sorcerer's Apprentice, Horvath pulls a move similar to that in the aforementioned Mummy Trilogy: he can shapeshift into a swarm of insects that form a rough human-shaped outlined before morphing back into himself.
Batman Begins has the Scarecrow and his fear toxin. In several induced hallucinations, the victim sees worms crawling out of the Scarecrow's eyes and mouth.
In the same film, the bats summoned by Batman to provide cover against Scarecrow's goons and the police for him to get Rachel out of Arkham.
In Dan Abnett's Gaunt's Ghosts novel Straight Silver, when Ghosts are traveling through a tunnel behind enemy lines, they are swarmed by rats. Although none of them are killed, most are bitten, and one, overrun, was bitten several times and deeply horrified.
The German novel Der Schwarm which translates literally into The Swarm features the Yrr, a collective of one-cell beings that live in the deep sea and can combine into intelligent beings. They try to eradicate humanity for destroying the environment.
The Edge Chronicles: Wig-wigs. They're small. They're fluffy. They have huge mouths with rows of razor sharp teeth. And there's hundreds of them.
"Leiningen Versus the Ants", a short story by Carl Stephenson, is about a Brazilian plantation owner who takes on a mass of army ants. Adapted for an episode of the Escape radio program, the movie The Naked Jungle, and even an episode of MacGyver.
"Sandkings", a short story by George R. R. Martin, which was adapted (with numerous changes) into an Outer Limits episode. Simon Kress, a rich and vain Jerkass whose hobby is collecting dangerous pets, stops into The Little Shop That Wasn't There Yesterday, and purchases four groups of the titular insectoids. The shopkeeper tells him that they will literally worship him by carving his likeness into their sandcastles, and the four "armies" will make war upon each other, for Simon's amusement. The shopkeeper also warns him to be patient, to give them time to grow and mature, and to treat them well. He isn't, and he doesn't.
The third book of A Series of Unfortunate Events has Lachrymose leeches, which swarm the poor fools who violate the 'Wait an hour before going swimming rule.
Remember The Bible's 10 plagues of Egypt? Plague #2 was frogs, plague #3 was gnats/lice/fleas, plague #4 was flies or wild animals (depending on the interpretation), and plague #8 was locusts.
And in the book of Revelation, one of the Trumpet Judgments is a swarm of demon locusts that infect people without the seal of God on their foreheads with a maddening delirium that lasts for five months.
Drog beetles in Galaxy of Fear. They're docile and harmless individually, but the more they are the more aggressive they act, and in large enough numbers they start going after people. In The Swarm a character peripherally notices that clouds are covering the sun, and in another moment realizes that those aren't storm clouds...
In another Star Wars Expanded Universe book, Planet of Twilight, there are the Droch beetles, who function on the microscopic level or who can evolve to a sentient, hominid form, the main villain of the book, who plots to use the Imperial Remnant to get the Droch off their homeworld and spread into the stars, but in their primary form are very much The Swarm.
The Swarm of Night from The Chathrand Voyages isn't one in the most technical sense (it's made up of millions of tiny black, bug-like spirits but all are part of the same entity and guided by the same purpose) but certainly resembles one enough to earn its name. It exists to patrol the border between the living world and the underworld, preventing either from troubling the other, but when loosed into the living world it becomes attracted to acts of death and violence (such as large battles) that are already in progress and "completes" them (by killing everyone left alive). This causes it to grow larger, and if it grows large enough, it can (and will) consume the entire planet. The Big Bad deliberately set it free so that his God of Evil patrons would be impressed enough by his destruction of a world to elevate him to godhood himself.
Nightworld. Portals to Another Dimension have opened sending nightmare creatures swarming across the Earth, including "chew-wasps" which have More Teeth than the Osmond Family, "spearheads" (a flying spike that impales and sucks out the victim's blood), "belly-flies" (floating sacs of acid) and "man-o-wars" (just think tentacles). Humanity barely has a grip on these horrors with steel mesh defenses and flamethrowers when even bigger monsters start coming through...
Stargate SG-1 Prior Bugs or R75 are made this by thoughtless research, Fridge Logic has the echolocation-prone death machine kill everyone and reproduce infinity-fold rather than thousand-fold but somehow avoid SG-1 and their special guests until they manage to beckon the Prometheus to teleport them into safety
The Sandkings, the first episode in the later 90s version of The Outer Limits are a swarm that digs through sand and builds things in them and... ITS FULL HORROR!!!
Smallville had an episode with a lady who could control bees.
The X-Files: in one of the most purely terrifying episodes ever aired (...in any series, ever), season one's Darkness Falls tells the story of a previously-unknown, multi-hundred thousand year old species of web-weaving insects that cocoon their animal victims before draining them of their vital fluids...and which only come out at night, as well, thus adding another primal fear to the situation. By the end, just how frightening were they...? When the forces of the Shadow Government, operating under the auspices of an environmental hazard unit, arrive and make it clear to a traumatized-by-attack yet slowly recovering Mulder that they will stop at nothing to end the creatures' threat...you realize that you're thanking God for the erstwhile fascists.
Infested is a Truth in Television documentary series about people's homes being overrun by spiders, ants, snakes, or other undesirable critters. While seldom lethal, such Real Life incidents can certainly render a property uninhabitable.
In Dungeons & Dragons, the way the rules are set up there's no logical way for bug-sized or even normal-rat-sized creatures to be properly threatening even to first level characters...hence, the Swarm type. Depending on the size of the individual creatures involved, swarms can resist and even be immune to damage that isn't an area attack.
In Fourth Edition, Druids have an optional class feature that lets them become one when Wild Shaped. Swarm Druids are extremely tough, enough to act as secondary defenders.
3.5 Druids have a Prestige Class called Swarm Lord. They can shapeshift into swarms and control them-normally swarms and vermin are off limits to druids.
Early editions of the "Creeping Doom" swarm summoning spell would inflict 1 point of damage per creature (that would then die) but could have up to 1000 creatures. 1000 points of guaranteed damage against any opponent vulnerable to standard attacks - such a swarm could easily kill a dozen first edition dragons.
Both Warhammer and Warhammer 40,000 have swarm units. They are typically represented by a large base with many models on it, counting as one multi-wounded model. They also tend to be cheap, so these swarms tend to be fairly big.
Tyranids from 40,000 have weapons that shoot a number of small creatures at an enemy to eat it to death.
Quite a few cards in Magic: The Gathering are meant to reflect this trope, but the Slivers do it best. In general terms, for each Sliver in play, all Slivers in play get stronger, whether just more powerful and tougher, or gaining new abilities.
The original Magic Swarm is Plague Rats, whose power and toughness were both equal to the number of Plague Rats in play. Long after the Obvious Rule Patch that limited copies of a single card to 4 per 60-card deck, they made an updated version called Relentless Rats.
In Traveller there is a small planet called Nifhleim that is completely covered with mysterious microscopic creatures(either biological or robotic). Anything that comes to the surface is devoured in hours.
Also Parasites, Scarabs, Tallon Crabs and Lumigeks in the original Prime. There's quite a lot of small weak enemies that appear in large numbers in the game. They're not quite as deadly as Ingstorms tho (doing only minor damage while Ingstorms will kill you really quick without the Light Suit).
Known derisively as 'blobbing' in EVE Online this is the primary tactic of the infamous Goonswarm alliance leading to their adoption of the Bee as an emblem. Don't let that fool you, the Goons have some very competent players and strategists but the alliance structure is such that the majority simply default to the 'Jihadswarm' approach.
In Dragon Age: Origins, Morrigan and other mages with the Shapeshifter specialization can become one. If they master their shapeshifting, they even can drain life from nearby enemies.
During one area of Ratchet & Clank Future: A Crack In Time, you have to avoid invincible swarms of tiny, jabbering critters called Tetramites. Unlike every other source of damage, Tetramites will constantly damage Ratchet and slow him down if they touch him. The creepy music that accompanies their appearance drives the point home that you've got only three options- shoot some water to repel them, use plant nectar to distract them, or run like hell.
In both Resistance Fall Of Man and Resistance 2: In the first one (only in a cutscene): crawlers, cockroach-like things that infect someone by getting in one's body en masse and in the second one: during a level, you are chased by an invincible swarm of flying, razor-sharp bugs(according to intel, evolved crawlers from the 1st game)that are invulnerable to boot.
Arachnophobics have been known to have a hard time getting through some levels of the Tomb Raider games. The latest one, Underworld, had swarms of spiders in the earlier levels that Lara had to shake off, and then human-sized tarantulas, that, once shot and killed, burst into a nausea-inducing mess that looks unsettlingly like what a dead tarantula might look like in real life.
Mass Effect 2. In the Suicide Mission, you must navigate through a corridor of Collector Swarms that will kill you. If you don't pick the right biotic for the job, one of your squadmates will be killed by the swarm. Shepard also runs for dear life back to the Normandy at the very end away from the swarm and other Collectors.
Haunting Ground: Failing the Truth Puzzle (the spot the difference rooms in Daniella's area) results in Fiona being locked in the room, with a swarm of beetles/scarabs flying in from the air vent to eat her alive. The last shot we see before the game over screen is of one crawling out of the human mannequin's mouth.
Yoshi's Story utilized this in several forms. In levels like The Tall Tower or Frustration, you get swarms of chickadees, flying by constantly. In the cloud level, you get bees in one room, and a much denser swarm of mini fly-guys in another. A huge swarm of mini cheep-cheeps is found in Lots o' Fish.
The Binding of Isaac expansion Wrath Of The Lamb introduces the Swarmer enemy, little more than a withered humanoid head serving as a nest for a cloud of flies.
While not a swarm of insects per se, the Swarm from Spiral Knights is this. Basically, it's a bunch of black particles that corrupt and infect anything they touch, including enemies. While traces of it can be found in Spark and Roar's last floor, most of the deadly substance is thankfully sealed away within the Shadow Lairs. Unfortunately, said Shadow Lairs are literally replicas of the boss levels, including the bosses themselves. Considering that the Swarm needs to infect something first to take its form, this implies something very dark... Thankfully, however, Knights are immune to it.
That's not even the worst of it; after beating the Swarm-infested bosses, you are sent into the Unknown Passage: an entire section of the Clockworks that serves as a sort of breeding ground for the monsters; this is also where the Swarm reaches it's highest concentration. To make matters even worse, it's implied that King Tinkizar is the one that created the Swarm, as there Gremlin corpses lying on the ground...
The nematodes in Sponge Bob Square Pants. They eat everything in their path - some kelp, a stop sign, a whole truck - then wash it down by sucking the juice out of SpongeBob's pineapple home.
Technically, Zaktan from BIONICLE, although he usually functions as The Worm That Walks. When his old boss tried to vaporize him, he was somehow able to pull himself back together as microscopic "protodites". In this new, permanent state, Zaktan can easily avoid attacks by turning into an insect swarm; change the shape of body parts; heal damage by filling the gaps with Protodites; and engulf a foe in an attack that must feel like getting hit with thousands of needles. Zaktan himself calls it a curse however, as his voice now sounds like a crowd speaking; and whenever he wakes up he can feel his body shifting "where there once were tissue and solid metal".
Don't forget the Bohrok. Actually called The Swarm.
Hymenoptera, the order of Insecta that includes bees, wasps, and ants, is responsible for more lethal attacks on humans than any other animal on the planet.
Among vertebrates, flocks of birds often use "mobbing" tactics to chase off predatory birds. Small songbirds do this to crows, and crows do it to hawks.
Sadly, many paranoid schizophrenics and meth addicts have delusions of insects coming out of their bodies to torment them, leading them to cut, scratch and otherwise hurt themselves to get rid of the insects that they imagine are there.
The largest swarm of organisms ever documented took place in the western United States in 1875, when Rocky Mountain locusts spread out from Texas to decimate agriculture in four states. Measurements of its scope and speed peg the swarm's area at some 198,000 square miles; modern entomologists calculate that it consisted of some 3.5 trillion insects.