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"Once I figured out these Sacktick things didn't like the cold too much, I shut off the generator - let the whole ship ice over. That did the trick, mostly."

The Sacktick is a parasite Synth enemy cut from Half-Life 2.[1]


  • The Sacktick was to be a macro virus created by the Combine. It was to be delivered by missile-like pods in numbers, generally to soften an enemy position before an assault.[1]
  • The Sacktick was to seek out organic hosts, on which it would feed and use as food for the next generation of ticks. In this way, a small number of ticks dropped into an enemy stronghold were to multiply and create a great number of individuals.[1]
  • Mouthparts were to be able to splay open, as part of a threat display. In addition, it was to make a clicking buzzing noise while bobbing its body up and down against the surface it would be attached to.[1]
  • The sack (the black growths on its both sides), whose use is not exactly known, was to be kept curled under the tick's body. Once fed, the sack was to unfurl behind the legs and dragged behind the tick.[1]
  • Its only known depiction shows the creature bearing markings similar to that of the Gunship, said to denote delivery vehicle and task group.[1]
  • As heard in the playable Half-Life 2 Beta sound files, Sackticks were originally to be thrown at the Borealis. Sackticks were to be unable to handle low temperatures, and Odell was to explain to Gordon that he was able to defeat them by shutting off the Borealis' generator, and let the ship ice over.[2]


Its delivery by missile-like pods is the only thing that made it into the final game, recycled as the Headcrab Shell.

List of appearances[]