The Swarm are the Marines' main and only enemies in Alien Swarm. They seem to be Humankind's main enemy and threat for quite some time, harassing their outer colonies. In Alien Swarm Source's first official campaign, Jacob's Rest, the Marines fight the Swarm through a mining colony that they have overrun.
There are many hostile forms of life to encounter in Alien Swarm. Care must be taken around many of these, for obvious reasons.
Technically not an enemy by itself, swarm Biomass blocks off access to areas and can only be cleared with the M868 Flamer Unit, Mining Laser, or other incendiary weapons. In either case, destroying the Biomass will call in the swarm - expect Drones and Rangers to come running. Coming into contact with Biomass will cause damage.
Bearing more than a passing resemblance to Half Life's Gonarch, the Boomer is a large tripedal creature that acts like a gigantic suicide bomber. If a Boomer is killed before it can inflate, it poses little threat to a team; however, if it does inflate, its death will result in the release of several explosives that detonate after a few seconds, inflicting considerable damage to nearby marines in the process.
A small flying insectoid often seen diving down from above, the Buzzer is a nuisance but not a significant threat by itself; it has little health and is capable of dealing only a minimal amount of damage over time on every difficulty level. However, they typically attack in groups and cause the screen to vibrate rapidly upon contact with the player character.
The most common of all the swarm types. Drones often attack in large numbers to compensate for their relative fragility. Although relatively susceptible to melee attacks, the Drone's claws can inflict considerable damage in few hits. Care should be taken to avoid letting them get close.
Technically harmless by themselves, swarm Eggs rapidly 'hatch' a Parasite if a potential host comes near. Killing Eggs before they hatch is top priority, since they are much larger targets than parasites. Fire is widely regarded as the most effective "treatment" for an Egg infestation. An Egg set on fire will promptly eject a burning parasite but does not count as having hatched.
Grubs are tiny, harmless lifeforms that present minimal threat to any marine forces. They can be killed by any form of gunfire, explosion, or by simply stepping on them. Guns cannot target them (except the Tesla Cannon), and they cannot hurt your team. Don't mistake them for Parasites.
Large red and white lifeforms, Harvesters periodically spit out tiny 'Spawn' lifeforms. Harvesters seem to have no attacks of their own and prefer to keep away from combat where possible. They are relatively easy to kill, but will launch out several more 'Spawn' upon death. Coming into contact with Harvesters will cause damage.
Tiny red and white spider-like creatures - not to be mistaken for Parasites - Spawn are produced by Harvesters, and their primary purpose is to launch themselves at hostiles - i.e., marines - killing themselves in the process. They are essentially tiny suicide bombs. While such Spawn inflict only fairly low amounts of damage alone, they are small, fast-moving, and can mob an unwary Marine. On Hard or Insane, they do a rather high amount of damage - a squad of at least 5-6 spawns can easily kill a marine on Insane, so caution is required.
Large but relatively weak support units, Mortarbugs spit a line of three highly explosive projectiles over long distances, like an upgraded version of the Ranger. These projectiles do not explode instantly, but instead stick to the floor or walls before exploding after approximately three seconds, dealing significant damage to anyone nearby. If not killed quickly, they can harass a squad and prevent them from gaining access to an area. Individual Mortarbugs are fairly weak and easy to kill (being essentially defenseless at short range) but, like Rangers, their main strength is supporting other members of the swarm, using their bombs to restrict marine movement or split the squad up.
One of the most potentially dangerous life forms, Parasites can infest a marine, obscuring vision and inflicting damage over time. If a marine dies whilst infested, they will spawn several additional Parasites that can rapidly infest an entire squad. Only medical equipment can effectively remove an infestation, though a v45 Electric Charged Armor can also remove them from the user's body. They are easily identified by several bright yellow parts on their body that make them easy to spot, even in dark areas.
One of the few swarm lifeforms with a ranged attack, Rangers launch a volley of acidic projectiles over moderate to long distances, harassing squads from afar. Individually, they are weak and their projectiles can be evaded by the quick-witted, though they can prove to be a nuisance in numbers or when supported by Drones.
Capable of absorbing vast amounts of damage compared to most bugs, Shieldbugs have massive, armoured limbs that give them their name. The best way to kill a Shieldbug is to attack it from behind, aiming for the yellow-white cluster on the rear of their body. Attacking from the front is ineffective and puts marines at risk of the Shieldbug's strong melee attack which can knock enemies away for a good distance. Ice, Fire and Electrical damage effects also help when fighting Shieldbugs. An electrically-stunned Shieldbug will not move much and is unlikely to attack, leaving it very vulnerable to even a meleeing marine. A frozen Shieldbug in comparison is completely immobile and incapable of attacking.
With the exception of the Shaman. All the unused alien models in the SDK including the Queen are from an earlier beta version of the game. They all use the same names as the current models. The Shaman is the only unused enemy that uses the release art style.
- Main article: Beta Aliens
In addition to the Swarm aliens featured in Jacob's Rest, there are several unused Alien models from the beta version of the game dating back to 2006.
|Biomass • Boomer • Buzzer • Drone • Egg • Grub • Harvester • Mortarbug • Parasite • Ranger • Shieldbug|
|Aliens • Alien Types • Beta Aliens • Queen • Shaman|
|Marines • Enemies • Classes • Playable characters • Weapons • Equipment|
Achievements • Challenges • Difficulty • Experience • Leveling • Promotion • Skills • Speed running • Strategy
Campaigns • Console • Custom maps • Maps • Mapping tutorials • Modifications • Patches • Server setup