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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 in an Aquarium in 'Crush Depth'

During the Resonance Cascade, Leeches were teleported to Earth, infesting the oceans. They seem to have caused the extinction of most earthly sea creatures. Indeed they are the only creatures commonly seen in the sea, though it is said that some creatures may remain, mosly crabs, though it is likely they are few in number.[2] Some Earth creatures remain in inland bodies of water, where insects and frogs can be heard (though it is likely they are also few in number, like the crabs).[3] Earth creatures such as seagulls have even turned to hunting them, as it is stated that they keep their numbers down. While leeches are commonly seen in freshwater bodies, Ichthyosaurs also seem to occupy freshwater bodies as well.[3]


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 that their population is kept down by seagulls and that they ate most of the crabs.

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 cannot be killed and will drain 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]


  • In Half-Life 2, if the player uses the console command "notarget" and goes venturing too far in the sea, the Leech will still attack the player. This is because the leeches are not real NPCs, but are rather models.


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

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