{{Youmayd|the enemy|the weapon|Barnacle Grapple}}
{{Enemy Infobox
| image=
| image2=FileBarnacle Ep2.jpg|125pxFileBarnacle HL1.jpg|125px
| name=Barnacle
| affiliation=
| type=Static; Ceiling-dwelling
| health=35
| weapons=*Crushing bite
*50, 10 second delay(''HL'')
*10, attacks repeatedly(''HL2'')
*Neck snap (''HL2'') (instant kill to NPCs only)
| entity=*monster_barnacle (''HL1'')
*npc_barnacle (''HL2'')
| designer=Ted Backman''Half-Life 2 Raising the Bar''
{{Quote|They were only able to coerce it into latching onto organic surfaces.|Black Mesa scientist|Half-Life}}

The '''Barnacle''' (Taxonomic designation ''Cirripedia donaldsonia'',http// Half-Life Monster of the Week Feature on or "Donaldson's Barnacle") is a stationary ceiling-dwelling alien, notable for its unique method of catching prey using its sticky "tongue".

A Barnacle is little more than a large mouth full of two rows of sharp teeth, with a long string-like appendage dangling out of its maw. This strand secretes a very strong natural adhesive that can bond to whatever it comes in contact with. The Barnacle uses its "tongue" to snare and lift prey items; the appendage is strong enough to support the weight of an adult human. 

Barnacles cannot differentiate between living and inorganic items that become stuck to their tongues, and can be tricked into hauling in barrels, pallets and other debris commonly found in their vicinity. Upon attempting to consume these items, the Barnacle will find them unpalatable and release them, showing that they can dissolve their own adhesives if need be. 

Barnacles attach themselves to ceilings or the undersides of overhangs, from which they lower their sticky tongues. Although Barnacles can be found in a wide array of environments, they seem to prefer damp areas. Curiously, while many Barnacles can be found infesting the Black Mesa Research Facility, few are encountered on Xen.

Barnacles are relatively weak; 5 shots from a 9mm pistol will kill them. They are most easily dispatched from a distance, although players who become ensnared by its tongue are usually able to kill them before being consumed. The Barnacles are weak against the crowbar, which in both games kills them in a single hit. (However, in Half-Life Day One,  four hits are required, which will be a fatal move for the player.) In any game, attacking a Barnacle which is high up with a crowbar is generally a bad idea, as you will take fall damage as well as the Barnacle's attack. In Half-Life, an undetonated hand grenade will kill a Barnacle instantly.  When killed, Barnacles typically disgorge bones and other remains of recently consumed victims.

In ''Half-Life Opposing Force|Opposing Force'', a scientist refers to removing a Barnacle from its "point of gestation". This suggests that a Barnacle will spend its entire life attached to the spot where it was born. Earthly barnacles use mobile larval stages and ocean currents to reach new growing areas; it is likely that Xen Barnacles use a similar means to spread. 

The name "Cirripedia donaldsonia" comes from its discoverer and first victim, Black Mesa scientist Louis Donaldson.

==Behavior and skills==
FileBarnacle Gordon.jpg|left|thumb|150px|Gordon Freeman being choked by a Barnacle in the Canals.

Barnacles are relatively simple creatures. They do not appear to possess any degree of intelligence--instead of actively hunting prey, they feed by reacting to external stimulus, in the form of animals which come into contact with the Barnacles' tongue. However, although the creatures do not demonstrate any intelligence in hunting, they possess an uncanny ability to attach themselves to ceilings overlooking thoroughfares frequented by potential prey, although some do seem to hide in corners far away from routes used by prey; the logical explanation for this is that Barnacles in less adequate conditions die out, while luckier creatures flourish. Similarly to real barnacles, they typically occur in groups or colonies. These are found throughout the entire ''Half-Life'' series, and the player often encounters small areas populated with large numbers of Barnacles, which do not seem to be in competition with each other.

Barnacles appear to be capable of killing and digesting a human being within only a few seconds, literally ''swallowing'' it, stripping the skeleton of flesh and spitting out indigestible bones. As the Barnacles are never seen moving, it can be assumed that their food requirements are relatively low and that they can survive for extended periods without food, perhaps explaining their sedentary lifestyle.

In the original ''Half-Life'', humans become immobilized when caught by Barnacles—although they struggle when wrapped in the creatures' tongues, captured humans appear to be incapable of fighting against the Barnacle when they reach the mouth, even though they are clearly still alive. It is possible to save an NPC from a Barnacle by killing it before he is consumed. The NPC will then simply drop, unharmed.

In ''Half-Life 2'', Barnacles take a few moments to differentiate between edible and inedible material. Consequently, objects such as tires, barrels or pieces of wood can be used to "distract" a Barnacle and allow a player to easily slip past it. In a similar fashion, by setting alight an explosive barrel at the right moment, a player can kill a Barnacle attempting to eat it (or even several closely-placed Barnacles). It also seems that the Barnacle tries to wrap its tongue around the target tight enough to break bones and kill it. This is based on the observation that birds as well as Resistance or Combine troops die before they even reach the main body, merely by virtue of being caught. Turning on closed captions and then being captured by the Barnacle reveals the sound file is called "Barnacle Neckbreak"; also, in a ''Half-Life 2'' concept art image, a Barnacle's tongue is seen wrapped around Gordon's neck, trying to strangle him. Gordon Freeman is unaffected by the tongue's crushing attempts, probably due to his HEV Suit's neck-covering extension. An alternative explanation might be that the tongue incapacitates the Barnacle's prey by means of some sort of paralyzing neurotoxin.

It is interesting to note the manner in which a Barnacle in ''Half-Life 2 Episode One'' deals with a Zombine after capturing a Zombine, the Barnacle will only eat the Headcrab attached to it, while the beheaded body is dropped. On the other hand, Barnacles have been recorded consuming the entire body of unaffected Combine soldiers. This could be considered evidence that Barnacles dislike the taste of rotting or decomposed flesh, and would be consistent with their rejection of decomposed bodies thrown at them by the player. A glitch might occur where the Barnacle kills a zombie of any type and throws the body to the ground. However, it will continue to pick it up and discard it until the body is moved.

In ''Half-Life 2 Episode Two'', Barnacles are seen trapping and eating Antlion|Antlions. They are also seen trapping Acid Worker Antlions, but as the Worker explodes as it is bitten into, this invariably results in the death of both parties.

An interesting fact is that the Barnacle will only eat what it identifies as a humanoid-type creature--both humans and Vortigaunt|Vortigaunts--if it latches onto the head. If it latches to the waist, leg, hand, etc. the Barnacle drops the body as if inedible, possibly because of the difficulty in consuming it in such position, or it doesn't recognize the shape due to latching on part of a body that is not the head or neck.

==Behind the scenes==
*According to Gabe Newell, the Barnacle was created as a way to constrict movement in dark areas of the Black Mesa Research Facility, suggesting its creation was quite recent in the game's development.

*The Coast chapters of ''Half-Life 2'' were originally to feature a Barnacle variation, the Sand Barnacle.Playable Half-Life 2 Beta|''Half-Life 2'' Beta files

*It appears that barnacles originally had ability to strike targets in ''Half-Life''.{{YouTube|W90QncBwtr4|Barnacle ''Half-Life'' Beta video}}


*It is possible to get an The Orange Box Achievements|achievement called "Barnacle Bowling" by killing a large group of them via explosive barrels.
*The top of the Barnacle can be seen in the Barnacle weapon worldmodel from ''Opposing Force''.
*In real life, the Earth creatures (or Cirripedia) is an arthropod related to crabs and lobsters.
*It is possible the Barnacle was inspired by a similar creature in Sierra's ''Space Quest III''. Native to a small rock cluster of Planet Phleebhut, they had a similar method of grabbing things with their tongues and determining whether or not something was edible (Terminator Robots, while not edible, would still be destroyed).wcspacequestPhleebhut Podsnatchers|Phleebhut Podsnatchers on Space Quest wiki
*A Hopper Mine that is picked by a Barnacle will explode when it is about to be bitten.
*Though in ''Half-Life'' the barnacle can only attach to organic surfaces, in ''Half-Life 2'' it will latch onto barrels, tires, and other man-made objects.
*If a Barnacle attempts to eat a Poison Headcrab, both the Headcrab and the Barnacle will die. This may not happen trough in the ''Half-Life 2'' before a update.
*In ''Half-Life'', Barnacles will eat almost all human NPCs--with the only exception being Female Black Ops-- only, while all other NPCs are unaffected when they touch the tongue. In Half-Life 2, Barnacles are capable of eating all NPCs and objects that come into contact with its tongue.
*In ''Half-Life'', Security Guard|Security Guards will ignore Barnacles even close enough to be able to shoot them. However, in ''Half-Life Source'', they will shoot them once they come across, albeit by shooting forward rather than upward, which curiously still results in a victimized Barnacle getting shot.

*If a Barnacle attempts to consume a Rollermine or Poison Zombie, the game will crash.
*The Overwatch Standard Issue Pulse Rifle's Energy Ball would not damage Barnacles. This has been fixed in an update; the ball will kill Barnacles in any game.
*If the player spawns Dr.Breen at the tongue of the Barnacle, the Barnacle will not swallow Breen whole unless he is killed by external means before reaching the Barnacle's body.


FileBarnacle concept.jpg|Concept art.
FileBarnacle concept clean.jpg|Ditto.
FileXen vista full.jpg|Concept art for Xen, including Barnacles.
FileBeta Barnacle closeup.jpg|Early close-up view.
FileInside Barnacle.jpg|Early screenshot showing Barnacle from inside.
FileSecurity guard in Barnacle.jpg|Barnacle eating a security guard.
FileBarnacle eating.jpg|Early screenshot showing Barnacle eating a security guard and an Alien Grunt at the back.
FileBarnacle eating2.jpg|Ditto.
FileXen cases BMRF.jpg|Xen flora and the Barnacle Grapple stored in cases in Black Mesa.
FileOf4a30000.jpg|Ditto, Fungus and Barnacle Grapple cases.
FileBa xen20003.jpg|Barnacles in a Xen grotto.
FileHl2 kill barnacleswithbarrel.png|The icon for the Barnacle Bowling achievement

==List of appearances==

*''Half-Life Day One'' {{1st}}
*''Half-Life Uplink''
*''Half-Life Opposing Force''
*''Half-Life Blue Shift''
*''Half-Life 2''
*''Half-Life 2 Raising the Bar''
*''Half-Life 2 Episode One''
*''Half-Life 2 Episode Two''

{{Imagecat|Barnacle images}}

CategoryXen creatures
CategoryHalf-Life Opposing Force
CategoryHalf-Life Blue Shift
CategoryHalf-Life 2
CategoryHalf-Life 2 Episode One
CategoryHalf-Life 2 Episode Two
CategoryTed Backman designs