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"I, eh, hope you like leeches."
The Fisherman[src]

The Leech, also known as Carnivorous Leech,[1] is an aquatic organism from Xen.


Leeches appear as small, agnathan like creatures that resemble leeches, specifically the terrestrial medicinal leeches. They also resemble lampreys, hagfish, and candirus, and are similar to those animals in ecological niche as well. They are usually white (sometimes pink or yellow) in color.

Leeches underwater OpposingForce 'Crushed Depths'

Leeches in an Aquarium in 'Crush Depth'

During the Resonance Cascade, Leeches were teleported to Earth, infesting freshwater and saltwater bodies. They seem to have been successful in establishing themselves, to the point that they may have caused the extinction most, if not all, of freshwater and marine fauna. Indeed they are the only creatures commonly seen in water bodies (in Half-Life 2, Leeches are only observed in oceans), though it is said that some creatures may remain, mostly crabs, which instead suffered from heavy population losses.[2] Some Earth creatures remain in inland bodies of water, where insects and frogs can be heard, meaning that Leeches were either completely absent or did not fully eliminate them.[3] Despite this, statements made by the fisherman say that Earth creatures such as seagulls have turned to hunting them, as it is stated that they keep their numbers down (as there may not be much for the seagulls and other predators of the leeches to eat in the first place due to the leeches themselves). While leeches are commonly seen in freshwater bodies, the Ichthyosaur also seems to occupy similar habitats, possibly showing non hostile coexistence between Xen fauna.[3]


Leeches aquarium

Leeches in an aquarium in the Biodome Complex.

Half-Life and its expansions[]

Leeches make their first appearance in Half-Life in some of the flooded sections of the Black Mesa Research Facility after the Resonance Cascade. In addition to being teleported to Earth, they are kept in the Black Mesa Biodome Complex for study. They appear to have six eyes.

Half-Life 2[]

In Half-Life 2, they attack Gordon Freeman in a swarm (an attack similar to that of the terrestrial piranha) if he ventures too far into the ocean, to prevent the player from venturing to the "end" of the map and force them to follow the proper path (much like the chopper in the video game Far Cry, for instance). Here the eye count is brought to only two.

Half-Life 2: Lost Coast[]

In Lost Coast, Leeches behave like in Half-Life 2. Furthermore, the Fisherman reveals that Leeches are used as food. Since ocean fish are now very rare or extinct, the human occupants of coastal areas seem to catch and eat Leeches instead. He also states they ate all the crabs, and seagulls keep their populations down.

Behind the scenes[]

  • In Half-Life, Leeches are minor enemies that do not cause much damage and can be easily killed. In Half-Life 2, they are not even scripted entities, yet areas infested with them will deplete the player's health in a matter of seconds.
  • The Ichthyosaur was originally intended to fulfill the role of keeping the player from venturing too far into the ocean. It can be encountered underwater in "d2_coast_02", among others, in the playable Half-Life 2 Beta, although it is only heard, not seen, before the player dies.[4]


  • Because Leeches are only models, they are not affected by the console command notarget in Half-Life 2.


List of appearances[]


  1. Half-Life 2 Prima Guide
  2. Half-Life 2: Lost Coast
  3. 3.0 3.1 Half-Life 2
  4. Playable Half-Life 2 Beta

External links[]