Ant Sight is a Fallout 3 perk. It is one of two possible perks you can get from Doctor Lesko for helping him get rid of the fire ant nest guardians, Ant Might is the other.
This perk grants +1 Perception and +25% Fire Resistance.
Ant Sight can be a very valuable perk because it greatly extends the range at which enemies show up as red tick marks on your radar, allowing you to stop, target them, snipe from afar, or otherwise prepare for them. Combined with a high Sneak skill level, this is a great advantage.