Fire ant

Fire ants are creatures living in the Capital Wasteland in 2277, and in the Mojave Wasteland in 2281. They are a variation of giant ants that have been genetically modified. Their name comes from their ability to breathe fire.

Background
 The fire ants of the Capital Wasteland were created by the scientist Doctor Weston Lesko, in a botched attempt to return giant ants to their normal size through genetic manipulation over time. His plan specifically was by way of injecting the eggs directly with the mutagen using his Protectron. However though his hubris he set up his experiment in a non-controlled environment and rushed his procedure, not only using FEV as a catalyst for mutation but also by injecting the Queen Ant directly. With a complete misunderstanding of the FEV believing it would last for years. One such mutation was their newfound ability to breath fire; specifically their venom became flammable and learned to ignite it with a spark made by clicking their mandibles. Upon discovery Dr. Lesko named it "pyrosis",  unbeknownst to Lesko the other mutation was increased intelligence.

With the ants increased intelligence they quickly expanded into the wasteland, first into Grayditch via Marigold station, overrunning the town and killing its inhabitants, sans Bryan Wilks. Writing the whole episode off as a "small error" and blatantly shrugging off the lives lost to his abominations both for saving more lives long term and for the betterment of science. In any case Those! ants may have been contained after the aforementioned quest of the same name. It is unknown how fire ants came to be in the Mojave Wasteland, it could have been a similar mutation to that of the fire geckos native to the southwest.



Fire ant nest guardian


Fire ant nest guardians are much harder to kill than any other type of fire ant. There are five of this kind of ant protecting the queen. Dr. Lesko refers to these ants as "The Queen's Quintet".

Fire ant soldier


Fire ant soldiers are the second lowest ranked ant in the fire ant colony. Their job is to protect their area from intruders. They are very aggressive and will attack humans, as well as other creatures on sight.

Fire ant warrior


Warrior fire ants are the predominant variety of ant you will encounter in the Marigold Metro tunnels in the Capital Wasteland.

Fire ant worker


Fire ant workers are the backbone for the ant community's infrastructure. As the name implies, they dig tunnels and care for the eggs. However, they will attack intruders if they are threatened.

Ant queen


Despite the fact that the rest of the colony has gained the ability to spit fire, the queen lacks this trait, it uses a ranged acid spiting attack instead. There is, however, an unused projectile cut from the game, which is a flaming version of the globs of spit the giant ant queens hurl at you, meant exclusively for this ant queen. It is plausible that this proves she was originally turned into a fire ant as well.

Appearances
Fire ants appear in Fallout 3 and Fallout: New Vegas.