Pheropods

"Bugbait" is the nickname Vortigaunts and resistance members use for the pheropods harvested from dead Antlion Guards and used to control antlions. Bugbait is highly valued in Antlion infested areas and some Resistance members on the coast travel considerable distances to reach the Vortigaunt Camp, where supplies of it can be obtained. Possessing pheropods prevents regular Antlions from attacking, as they are fooled by the scent into believing you are an Antlion Guard. However, other Antlion Guards are not fooled.

Usage
More a tool than a true weapon, a human in possession of pheropods can nonetheless use them to very deadly effect, as they can command regular Antlions. They literally become the pheropod holder's private army.

Pressing the primary fire button throws a pheropod, while secondary fire squeezes the pheropod to summon nearby antlions to your side. Throwing a pheropod at an object or location will cause it to splat and form a small cloud of pheromones, identifying it as a target. You can use this to command your Antlions to go to a specific place or attack a specific target.

Other information
When you throw a pheropod it is destroyed and cannot be used again. Even so, Gordon's supply of them appears to be infinite. It is unknown how stocks of them are replenished.

Whenever you encounter an Antlion Guard when in possession of the Bugbait, regular Antlions are nowhere to be found, so it's unknown whether they can tell the difference between you and a "real" Antlion Guard.

Whether Antlions consider you friend or foe appears to be determined by a trigger in the level itself, not whether you possess any bugbait or not, so even if you use cheats to get bugbait in chapters you're not intended to have it, Antlions will still attack.