Archives of Nethys

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Building the Swarm

Swarm Mechanics

Source Starfinder #43: Icebound pg. 52
When building a Swarm component using the monster creation rules (Alien Archive 126), keep the following points in mind.
Array: A significant majority of Swarm components use the combatant array, as they are tough creatures that rely on brute force. Specialized components might use the expert array, and only components that rely on psychic powers use the spellcaster array.
Alignment: All Swarm components are chaotic evil. Even the hive mind’s most calculated strategists pursue rapacious and destructive goals. They aren’t beholden to a sense of fair play and follow no authority other than the hive mind.
Creature Type: Swarm components are always monstrous humanoids, regardless of their appearance or function.
Creature Subtype: The swarm subtype applies to clouds or creeping collections of very small creatures; it doesn’t represent Swarm creatures. A cloud of tiny Swarm components might congregate as a swarm and have the swarm subtype, but there isn’t a specific subtype for Swarm components.
Other Grafts: Swarm components virtually never have class grafts, and only the strangest of circumstances would result in one with a template graft.
Senses: Swarm components bear antennae that allow them to detect subtle atmospheric changes. All but the weakest components have blindsense (vibration) out to 30 feet, and powerful ones might have blindsense out to a longer range.
Defensive Abilities: All Swarm components belong to the hive mind, and each has the following universal creature rule.
  • Swarm Mind (Ex) Members of the Swarm are bound together into a singular hive mind by a blend of exuded pheromones, imperceptible movements of antennae and limbs, electrostatic fields, and telepathic communication. All Swarm creatures within 30 feet of each other are in constant communication; if one is aware of a threat, all are. (Such awareness can spread along a chain of Swarm creatures under appropriate circumstances, potentially alerting distant Swarm creatures.) In addition, once per round when within 30 feet of another Swarm creature, a Swarm creature can roll twice and take the better result on a saving throw against a mind-affecting effect.
Immunities: All Swarm components are immune to acid and fear effects. Their own bodies circulate acid, so caustic chemicals don’t affect them, and the hive mind has no place for fear, having excised it entirely. These immunities, along with the Swarm mind defensive ability, are grouped together as a single special ability when assigning special abilities to a monster you’re creating. It’s not unusual for Swarm components to have other immunities (or resistances), depending upon their function.
Languages: Swarm components speak Shirren (or, perhaps more appropriately, shirrens speak the original language of the Swarm) and have telepathy out to 100 feet.
Special Abilities: Swarm special abilities generally fall into one of two types: physical or psychic. Physical abilities are those resulting from the component’s unique physiology, such as the arm-mounted acid cannon of a corrovox, the vicious arm blades wielded by a thresher lord (Alien Archive 110), or the trepanning spike of a mindreaper (Alien Archive 2 122). Many Swarm components inflict poison with stingers or barbs. Ranged physical attacks most often deal acid damage, but this isn’t a rule; a nauphage (Starfinder Adventure Path #20: The Last Refuge 60) fires globs of electrically charged adhesive. Psychic attacks need not be represented with spells or spell-like abilities; many Swarm components can assail the minds of their foes with psychic abilities that are powerful in effect but limited in scope. Examples include the corrovox’s disorienting mental chatter, the synaptic shriek of a psychovox (Starfinder Adventure Path #24: The God-Host Ascends 59), or the parasitic psychic siphoning of a xersk (Alien Archive 3 106).
Spells: Those rare Swarm creatures with actual spellcasting have spell-like abilities rather than spells like a spellcaster PC. Their spell-like abilities should include—and perhaps be limited to—mind-affecting spells. Spells that aren’t mind-affecting should fit the specific component’s theme; for example, the xersk has numerous staring eyes and a master Perception skill, so it also has see invisibility as a constant spell-like ability.