Those!

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

A lost, small boy called Bryan Wilks asks you to help him find his father, who seems to be trapped in Grayditch infested with fire-spitting giant ants. During two first stages of the mission Bryan will be hiding in Pulowski Preservation Shelter near the diner.

Find Bryan Wilks's father
The boy will approach you in the area outside the Super-Duper Mart. The boy and his dad along with other dwellers were attacked by fire 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 together with some ammo off the shelf in the house and the shack's key from Bryan's father body. In the shack you can find Doctor Lesko's equipment and terminal. Read the notes on the terminal to receive the Marigold Station location and the option to proceed there to locate the source of the fire ants.

Find the source of fire ants
In the Marigold Metro Station you need to find the cause of fire ant infestation. Instead you will find Doctor Lesko working down in a maintenance room. He explains you the reason of ant's behavior and how they gained ability to "spit fire". You can choose to help him reverse the effect or deal with the queen yourself. If you follow his instructions and kill only the Fire Ant Nest Protectors guarding the queen you will receive a prize - a choice of either the Ant Might or the Ant Sight perk. With a speech check you can kill the Ant Queen and still get the perks. You can also hold off killing the queen until after you choose your prize, then run down to the queen and kill her if you want to. At that point Doctor Lesko will also be running around in the queen's chamber, making a possible second target. Afterward, if you talk to Doctor Lesko he seems oblivious to the queen's death and not upset at all toward you. If you frenzy the queen she will attack the robot and he will help you kill her. Another easy way to kill the Ant Queen is to get close to her with a melee weapon and continue circling around her behind while attacking.

When speaking with Doctor Lesko about doing the ants task, if you ask for a "serious incentive", he will offer his old lab coat along with the ant perks. Lesko's Lab Coat provides +20 Radiation Resistance and +10 Science.

If you kill Doctor Lesko you lose Karma. On his corpse is a 10mm pistol and the password to his computer, as well as a +5 Science lab coat.

If you hack Doctor Lesko's terminal near the ant queen (don't forget to grab the Big Book of Science beside the terminal), you can send the Inhibitor Pulse yourself and destroy the mutagen sample he is using (FEV). If you choose to destroy the mutagen sample, you will need to tell him coming back. You can convince him with a Speech check, or sufficient science skill, that it was for the best. The rewards for the quest seem to be the same, although you gain more karma for destroying the sample and convincing Doctor Lesko that it was the right thing to do. If you miss the Speech Check Doctor Lesko voids your reward, to which you can promptly answer with a minor dose of lead for a dose of negative karma.

Find a place for Bryan Wilks to stay
Bryan will tell you his aunt Vera owns the hotel in Rivet City. You just need to ask her about Bryan Wilks and she'll agree to take him in. You will need to go back to Grayditch and tell Bryan he can move in with his aunt.

It's also possible to convince the mayor of Little Lamplight to let him stay there.

Alternately you can go to Paradise Falls. Talk to Eulogy Jones, and tell him you have a child for sale. He will offer 100 caps initially, but you can give him a Speech for 300. He will give you a collar to put on the person. You then trick Bryan into putting on the collar, and explain that it will guide him home. The quest will be completed, XP given, and caps from Eulogy. This however obviously gives a good bit of negative karma.

Bugs

 * None of the Fire Ants inside Marigold station are affected by the Inhibitor Pulse.
 * Fire Ant Nest Protectors may attack each other when injured simultaneously by grenade thrown in stealth attack.(This is most likely NOT a bug, since the blast area of explosives could criple the antenae/inhibitors of multiple opponents)

Behind the scenes

 * This quest was inspired by the 1954 film Them! also featuring giant ants.