Those!

 is a Fallout 3 quest. It is also an Xbox 360 achievement.

A lost, small boy called Bryan Wilks asks you to help him find his father, who seems to be trapped in Springvale, while he takes refuge in a diner.

This quest was inspired by the 1954 film Them!.

Find Bryan Wilks's father
The boy and his dad were attacked by Giant Ants. The father can be later found dead in his house by the shack, killed by the ants. You can loot a Chinese Assault Rifle off his body.

The mission after this is in the marigold subwaystation to the north where the fire ant infestation have to be cleared. Here you need to find the doctor who is in a maintenance room. You can choose to not follow his mission and destroy the queen, but if you follow his instructions, and kill only the fire ants (nested in the hatchery, go inside the room where the doctor i located), you will receive a prize in the form of increased strength or perception, among other things.