Generated by the infestation pit, the swarm host burrows into the ground in order to provide a seemingly endless supply of locusts. The large, mushroom-shaped structure on the swarm host’s back is a breeding ground that weaponizes the millions of diminute larvae inhabiting the creature’s acidic bloodstream. Through a simple system of membranes for matter exchange, glands that pump the offspring full of hormones to hyper-accelerate growth, and ducts for efficient transportation to the bubbling pockets on the surface of the incubator, the swarm host births deadly, short-lived locusts to destroy threats to the Swarm. The larvae also feed on damaged tissue, sealing wounds, and destroying anything foreign that enters their domain. When the creature is threatened or engaged in combat, a subtle chemical reaction signals the larva to head for the incubator, where they are evolved into living weapons.
The swarm host is often used in defensive maneuvers. Its legs boast powerful muscles that allow them to vibrate at hypersonic speeds, not unlike the teeth of the nydus worm. Despite that, the creature couldn´t burrow fast enough to adapt to shifting battlefield conditions. To correct this, a set of fragile (albeit regenerating) capillaries was put into place. Now, when the swarm host digs, the capillaries break and the creature’s acid blood softens the soil, allowing it to go underground in seconds. Flexible osseous structures of varying thickness slide and lock into position when the swarm host prepares to strike. Bearing a resemblance to siege tank hydraulics, this specialized skeletal system allows the swarm host to maintain position and balance when spewing locusts or when under heavy fire. The swarm host lacks mobility however, which leaves it vulnerable to quicker enemies with area damage like the hellion. 
The first swarm hosts encountered by the Swarm were primal zerg on Zerus, used against Kerrigan's forces by the pack leader Brakk. Swarm host strains were incorporated into Kerrigan's Swarm soon afterwards by Abathur, adapted through primal essence.
The swarm host can burrow without the upgrade. Classified as a siege unit, it endlessly spawns waves of locusts while burrowed: each wave consists of two locusts, and these are produced every 25 seconds. The locusts last 15 seconds (25 with an upgrade). This allows the zerg to better besiege entrenched enemy positions. They are produced via the hotkey "C".
Swarm hosts cannot attack directly.
In Legacy of the Void, swarm hosts can produce locusts on the move; this ability is now manually activated. These locusts are more powerful but do not spawn as quickly. In the late game the locusts can fly over terrain. The locusts must then "swoop" to attack.
Increases the lifespan of locusts by 10 seconds (to 25 seconds).
Heart of the Swarm CampaignEdit
Swarm hosts appear as primal zerg enemy units in Waking the Ancient. Afterwards, the player gains access to them in "The Crucible." They have access to a number of upgrades in the evolution pit.
In the campaign swarm hosts function much differently. They do not burrow, instead using the root command. While rooted, a swarm host cannot move but is still visible. They do not autocast spawn locusts in the same way as in the multiplayer game. Instead, they only spawn locusts, while rooted, when an enemy comes into range, or the player selects spawn locusts and clicks a location.
They do not burrow all the way into the ground, allowing them to be attacked without detection, however one of the upgrades available to the swarm host as well as one of its evolutions allows it to fully burrow itself.
- Burrow: Swarm Hosts can now burrow into the ground, preventing them from being seen by enemies without detection while still being able to spawn Locusts.
- Rapid Incubation: Locusts spawn 20% faster.
- Pressurized Glands: Locusts can attack both ground and air units.
The following section contains information from a previous version of StarCraft II which is no longer valid.
- Main article: Infestor/Development
The swarm host was expected to be available in the campaign and map editor of StarCraft II. As the swarm host is now, it could have been an aerial unit, but it eventually became a ground one. The idea behind its current design was to give zerg players their own siege unit, but make sure it functioned in a different manner to the siege tank or colossus.
The swarm host's current form was to give the zerg a new aesthetic, something to distinguish the unit from the usual claws and teeth that other zerg units possess.
|Zerg Units and Structures of StarCraft II|
|Heart of the Swarm|
|Primal Zerg Breeds|