Queen ant's hatchery is a cave system that can be accessed from Marigold Station.
The ants here are mutated fire ants, created by Doctor Lesko in a failed attempt at reducing their size. You will be sent here during the quest "Those!".
On Doc Lesco's desk/table can be found a filtration/containment unit, within which can be found a sample of his own mutated strain of the FEV virus.
The queen ant's hatchery is accessed through a hole in the Marigold Metro tunnels, near Dr. Lesko's makeshift laboratory. The hatchery is a straightforward, yet winding tunnel that's peppered with ant refuse piles and five guardian ants patrolling the area. The tunnel ends with the ant queen's main chamber with the Marigold ant queen in the back. There is a table with a terminal and scientific contraption on it that controls sonic pulses Lesko has developed to combat ant attacks.
The queen ant's hatchery appears only in Fallout 3.