npc_headcrab is a point entity available in 
Half-Life 2 series and 
Black Mesa.
These are the classic, slow-moving headcrabs. They attack by jumping at the player's head and inflict a nominal amount of damage. Almost any weapon can dispatch them easily.
Commonly found attached to a zombie host body, they will detach if that host is sufficiently damaged below the head.
There are several other headcrab variants and associated zombie types.
See also env_headcrabcanister which is a mortar shell containing a payload of headcrabs. The mortar shell inflicts damage within a radius of where it lands and releases headcrabs after impact. Triggers and entity options offer control over impact damage and when the headcrabs are released, among other options.
Placement Tip:Classic headcrabs can be paired with their fast-moving or poisonous relatives to make it more interesting.Placement Tip:Avoid the cliche of placing headcrabs in vents; they would likely be more of an annoyance than an improvement on gameplay.
Bug:If a headcrab is burrowed, using inputs or command that would kill it like sethealth 0 or npc_kill npc_headcrab does not work. They get ignored and the headcrab's health doesn't change. (tested in: Half-Life 2)Keyvalues
- Name (targetname) <string>
- The name that other entities refer to this entity by, via Inputs/Outputs or other keyvalues (e.g.
parentname or target).
Also displayed in Hammer's 2D views and Entity Report.
BaseHeadcrab:
- Start burrowed (startburrowed) <boolean>
- Should this npc start burrowed? Will unburrow via input or if an enemy gets near.
BaseNPC keyvalues
Expand
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CBaseCombatCharacter:
- Relationship (Relationship) <string> !FGD
- <string|targetname or classname> <string|disposition> <int|rank>
- Changes whether this entity likes or dislikes certain other things. Used like the ai_relationship entity, with this entity as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
- Physics Impact Damage Scale (physdamagescale) <float>
- Multiplier for damage amount when this entity is hit by a physics object. With a value of 0 the entity will take no damage from physics.
CAI_BaseNPC:
- Target Path Corner (target) <targetname>
- The path_corner that this NPC will move to after spawning.
- Squad Name (squadname) <string>
- NPCs that are in the same squad (i.e., have matching squad names) will share information about enemies and will take turns attacking and covering each other.
- Hint Group (hintgroup) <string>
- Hint groups are used by NPCs to restrict their hint-node searching to a subset of the map's hint nodes. Only hint nodes with matching hint group names will be considered by this NPC.
- Hint Limit Nav (hintlimiting) <boolean>
- Limits NPC to using specified hint group for navigation requests. Does not limit local navigation.
- Sleep State (sleepstate) <choices>
- Holds the NPC in stasis until specified condition. See also Wake Radius and Wake Squad.
- 0: None
- 1: Waiting for threat
- 2: Waiting for PVS
- 3: Waiting for input, ignore PVS
- 4: Auto PVS
- 5: Auto PVS after PVS
- Wake Radius (wakeradius) <float>
- Auto-wake if player comes within this distance.
- Wake Squad (wakesquad) <boolean>
- Wake all of the NPCs squadmates if the NPC is woken.
- Enemy Filter (enemyfilter) <targetname>
- Filter entity to test targets against.
- Ignore unseen enemies (ignoreunseenenemies) <boolean>
- Prefers visible enemies, regardless of distance or relationship priority.
DamageFilter:
- Damage Filter (damagefilter) <targetname>
- Name of the filter_damage_type entity that controls which entities can damage us.
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Flags
Start hidden : [65536]
Start hanging from ceiling : [131072]
ExpandBaseNPC flags
Wait Till Seen : [1]
- Prevents this NPC from seeing (or being seen) until it enters a player's viewcone.
Gag : [2]
- Won't make IDLE sounds until it's angry.
Fall to ground (unchecked means teleport to ground) : [4]
Drop Healthkit : [8]
- Causes this NPC to drop an item_healthvial upon dying.
Efficient : [16]
- Don't acquire enemies or avoid obstacles
Wait For Script : [128]
- Forces this NPC to "wait" in an idle state until it finishes playing a scripted_sequence.
Long Visibility/Shoot : [256]
- By default, increases a NPC's sight range to
6,000 units and allows it to attack from anywhere within that distance.
Fade Corpse : [512]
Think outside PVS : [1024]
- Allows this NPC to run its regular AI outside of any player's PVS.
Template NPC : [2048]
- Marks this NPC as a template for entities like npc_template_maker. The NPC will not spawn on its own. This is not needed for point_template.
Do Alternate collision for this NPC (player avoidance) : [4096]
NoteThis flag is disabled in 
episodic for player companions, because the StartScripting input does this.Don't drop weapons : [8192]
Ignore player push : [16384] (in all games since 
)
- Entity won't give way to player.
Inputs
- Burrow !FGD
- Burrow. If no burrow points within 512 units, does nothing.
- BurrowImmediate !FGD
- Burrow immediate.
- Unburrow !FGD
- Unburrow.
- StartHangingFromCeiling
- Start hanging from ceiling.
- DropFromCeiling
- Drop if hanging from ceiling.
ExpandBaseNPC inputs
CAI_BaseNPC:
- ActivateSpeedModifier !FGD
- DisableSpeedModifier !FGD
- Break
- Smash into pieces. If this is not possible, disappear.
- BecomeRagdoll (in all games since )
- Remove itself and instantly become a ragdoll with zero force (just go limp). OnDeath, etc. outputs will NOT be fired.
- ForceInteractionWithNPC <string> <string> (in all games since )
- Force the NPC to use a dynamic interaction with another NPC. Syntax is <targetname> <dynamic interaction>.
- ForgetEntity <targetname>
- Clears out the NPC's knowledge of a named entity.
- UpdateEnemyMemory (in all games since )
- Update (or create) this NPC's memory of of the given entity.
- GagEnable
- GagDisable
- Gagged NPCs won't speak (or moan, caw, etc.) unless made to be a choreographed scene.
- HolsterWeapon (in all games since )
- UnholsterWeapon (in all games since )
- Force the NPC to holster or unholster their weapon. Ignored if the NPC is scripting or if the NPC doesn't use weapons.
- HolsterAndDestroyWeapon (in all games since )
- Same as
HolsterWeapon, except the weapon is destroyed once it has been concealed.
- IgnoreDangerSounds <float>
- Ignore danger sounds for the specified number of seconds.
- InsideTransition !FGD
- OutsideTransition !FGD
- SetBodyGroup <integer>
- HACK: Sets this NPC's body group (from 0–n).
- SetEnemyFilter <string>
- SetHealth <integer>
- Set the NPC's health.
- SetMaxLookDistance <float> (only in
)
- Sets the maximum look distance for the NPC. Defaults are 2048 and 6000 for long range NPCs.
- SetRelationship <string|targetname or classname> <string|disposition> <int|rank>
- Changes whether this NPC likes or dislikes certain others. Used like the ai_relationship entity, with this NPC as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
- SetSquad <string>
- Change the name of this NPC's squad. Leaving the parameter blank will remove the NPC from any existing squad.
- StartScripting
- StopScripting
- Enter/exit scripting state, where NPCs ignore a variety of stimulus that would make them break out of their scripts. They ignore danger sounds, ignore +Use, don't idle speak or respond to other NPCs' idle speech, and so on.
- Wake
- Wakes up the NPC if it is sleeping.
CBaseCombatCharacter:
- KilledNPC !FGD
- Tells the entity it killed something. Despite the name, this can include a player. This input will be automatically sent by the victim when they die.
- physdamagescale <float>
- Scales damage energy when this character is hit by a physics object. With a value of 0 the NPC will take no damage from physics.
DamageFilter:
- SetDamageFilter <string>
- Sets the entity to use as damage filter. Pass in an empty string (no parameter) to clear the damage filter.
Outputs
BaseNPC Outputs
Expand
- OnDamaged
- Fired when this NPC takes damage (!activator is the damage inflictor).
- OnDamagedByPlayer
- Fired when this NPC is hurt by a player (!activator is the attacker or vehicle driver [if friendly fire]).
- OnDamagedByPlayerSquad
- Fired when this NPC is hurt by a player OR by one of the player's squadmates (!activator is the attacker or vehicle driver [if friendly fire]).
- OnDeath
- Fired when this NPC is killed (!activator is the killer).
- OnDenyCommanderUse
- Fired when this NPC has refused to join the player's squad.
- OnForcedInteractionAborted
- Fired when the NPC aborts a forced interaction for some reason (target NPC died, couldn't be pathed to, etc.).
- OnForcedInteractionStarted
- Fired when the NPC starts a forced interaction.
- OnForcedInteractionFinished
- "NPCs in actbusies can no longer perform dynamic interactions."
Todo: What does this mean?
- OnHalfHealth
- Fired when this NPC reaches half of its maximum health.
- OnHearCombat
- Fired when this NPC hears combat sounds.
- OnHearPlayer
- Fired when this NPC hears the player.
- OnHearWorld
- Fired when this NPC hears a sound (other than combat or the player).
- OnFoundEnemy <targetname>
- Fired when this NPC establishes line of sight to its enemy.
- OnLostEnemy
- Fired when this NPC loses its enemy. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
- OnLostEnemyLOS
- Fired when this NPC loses line of sight to its enemy.
- OnFoundPlayer <targetname>
- Fired when this NPC establishes line of sight to its enemy, and that enemy is a player.
- OnLostPlayer
- Fired when this NPC loses its enemy, and that enemy was a player. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
- OnLostPlayerLOS
- Fired when this NPC loses line of sight to its enemy, and that enemy is a player.
- OnSleep
- Fired when this NPC enters a sleep state.
- OnWake
- Fired when this NPC comes out of a sleep state.
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Dedicated Console Variables
Only in Black Mesa 2012. Requires
this texture to display properly as the texture has been removed.
| Cvar/Command |
Parameters or default value |
Descriptor |
Effect |
| sk_headcrab_health |
|
int
|
A headcrab's spawn health. |
| sk_headcrab_melee_dmg |
|
int
|
Melee damage. |
| g_debug_headcrab |
|
bool
|
Toggle headcrab debugging. |
| sk_headcrab_min_jump_dist |
|
int
|
Headcrab min jump distance. Only in Black Mesa 2012. |
| sk_headcrab_max_jump_dist |
|
int
|
Headcrab max jump distance. Only in Black Mesa 2012. |
| sv_headcrab_can_latch_on_player |
|
bool
|
Toggles headcrab's ability to attach player's head (if player catches it with head). |
See also
Class hierarchy