Giant Ants are the mutated descendants of pre-war ants, having grown exponentially over the last 200 years.
Although Giant Ants did not appear in the main Fallout: Equestria, they have made appearances in other stories.
Fire ants, collectively called Dragon Ants in the moohave are a form of mutated wildlife, encountered in the Moohave wasteland around New pegas. Dead-Shot encountered Dragon Ants on his way to an NCR/New Coltifornia Republic Outpost to seek aid and help for the troops at Slimm. The Dragon Ants surged forth to attack Dead-Shot who had to turn his fight into a running battle to defeat a dozen Dragon Ants.
Dragon Ants work as group hunters, attacking one will alert nearby Dragon Ants who will attack in numbers and force an attacker to retreat or be swarmed by the aggrivated Ants. Dragon Ants notably infest the Ivannapony area.
Dragon Ants get their name and infamous reputation due to their ability to breathe fire. They can communicate and coordinate attacks on potential attackers, forcing their prey to continually move or be swarmed by superior numbers. Their meat is very high in protein and they occasionally have a jelly beneath their carapaces that acts like a temporary boost to a user.
As mentioned in their biology, the majority of Dragon Ants are capable of breathing fire.
In Outlaw, Mach discovers an ant colony beneath Springvale school that a group of Raiders occupying the school accidentally breached as they were tunnelling underground, they are killed relatively easily from machinegun fire.
Tales of a Courier
There was a Giant Ant colony between Buckwheat and Westwood which Clover and Ace had to go through. The Ant Queen had been killed earlier by some Federation troopers that were captured and eaten by the queen. One of the ants, a fire ant, identifies Clover as its new queen and becomes his follower/pet.
The come in various size and types, including a small fire ant and a large soldier. Their eggs are coated in slime and they identify friends and foes via pheromones and scent.
Notes & Trivia
Giant Ants are based on the creatures from the Fallout series, in particular Fallout 3 & New Vegas.
The giant ants Mach uncovers under Springvale school are a reference to giant ants in Fallout 3, also encountered under a school with the same name.