Alien Swarm Parasite

The Alien Swarm Parasite is an unlockable headwear item for all Classes. It is obtained by earning the Hat Trick Achievement in the game Alien Swarm.

Trivia

Hat Trick Achievement Icon

• The Hat Trick achievement is earned by completing 2 co-op missions online.
• This is the second hat that appears to be a still-living creature, the other being the Triboniophorus Tyrannus.
• The earliest report of finding the hat can be found here.
• The Parisites tail has Jiggle Bones making it the second promotional hat with jiggle bones, the other being Max's Severed Head.
• The achievement picture shows a heavy with the hat.
• This is the only hat requiring you to get an achievement in a game besides Team Fortress 2.