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 ants have a hard, red-orange carapace that protects their body from environmental factors. They live in enormous underground colonies where they eat, sleep, and mate with the queen. Fire ants are omnivorous, using their pyrosis to kill live prey, but also eat what little vegetation they can find, when necessary.
Fire ants like to attack from range with a fire breath attack (which has surprisingly long range). The ants seem to have a minimum range at which they could breathe fire. If you get extremely close to the ants, they will constantly try to move backwards, letting off a spurt of flame or two. Additionally, they have a slow turn speed.
If their antennae is hit and crippled, they will become frenzied. Once a fire ant becomes frenzied, it will attack other nearby fire ants and other non-player characters. Once attacked by another ant, the attacked ant will return fire, damaging the attacking ant.
Due to their high fire resistance, fire damage based weapons like the flamer and the Shishkebab will have little effect on them.
Fire ant nest guardian
Fire ant nest guardians are unique versions of fire ant warriors. There are only five of these ants protecting the queen. Dr. Lesko refers to these ants as "The Queen's Quintet".
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. They are relatively easy to defeat at a medium level.
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. They are relatively weak compared to fire ant soldiers.
This ant queen found in the queen ant's hatchery. Like others in the game it is slow and has a ranged acid spitting attack that does a fair amount of damage. She cannot spit fire because Doctor Lesko's experiment affected only latter generations of ants. The queen has a very high amount of HP and is considered a "boss" enemy in the game.
↑The Lone Wanderer: "Experiments? What do you mean?" Weston Lesko: "My experiments are of a complex nature and would take a scientist to explain... oh wait! I'm a scientist! How marvelous! My foray into reducing the girth of these insectoid creatures is of utmost importance. I intend to generationally reduce their immense stature by way of a pre-birth induced mutagen. Isn't that clever?" (Weston Lesko's dialogue)
↑The Lone Wanderer: "Okay, now how about explaining that for the slower people?" Weston Lesko: "Hmmm. Let me see. Well... You start with a generation of very large ants. You simply inject the current brood's eggs with an engineered mutagen. Then, the next generation should be smaller. Do it enough times, and you may be able to reduce them back to their once original tiny size." (Weston Lesko's dialogue)
↑The Lone Wanderer: "I'm shocked you didn't attempt this in a controlled environment first." Weston Lesko: "Your knowledge of experimental procedure surprises me! Indeed, I have skipped a step and directly modified an entire brood. Perhaps I was too hasty... I was so certain it would work. To correct this mistake, I'll need to get to my terminal to modify the mutagen." (Weston Lesko's dialogue)
↑The Lone Wanderer: "So all that needs to be done is eliminate the remaining Ants?" Weston Lesko: "I'm afraid it's not that simple. The mutagen has already been injected into the Ant Queen. She has enough in her body to last for years. My problem right now is I can't reach my terminal to make the proper adjustments and repair the damage I've caused." (Weston Lesko's dialogue)
↑The Lone Wanderer: "So, what's gone wrong?" Weston Lesko: "Well. I'm afraid I've made slight miscalculations in the mutagen. Instead of lowering their size, the brood hatched with a new biomechanism. I call their genetic abberation pyrosis; the ability to emit flame from their bodies. I may be able to correct this error, but I can't get near my equipment." (Weston Lesko's dialogue)
↑The Lone Wanderer: "Are you aware your new ants breathe fire?!" Weston Lesko: "Well, this is rather embarrassing so you'll have to forgive me, it appears that I've made a slight miscalculation in my mutagen samples. Instead of lowering the size of the ants, the brood hatched and developed a new biomechanism. I call their genetic aberration pyrosis; the ability to emit flame from their bodies. I may be able to correct this error, but I can't get near my equipment." (Weston Lesko's dialogue)
↑The Lone Wanderer: "I've got news for you, brainiac. It ain't working." Weston Lesko: "Hmph. I don't expect a common Wastelander to understand the intricacies of an experiment this delicate. There was an error in my calculations that caused my mutagen to allow the ants to develop a new biomechanism. I call their genetic aberration pyrosis; the ability to emit flame from their bodies. I may be able to correct this error, but I can't get near my equipment." (Weston Lesko's dialogue)
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