Sure they dont have eyes? Those in the pics are holding their heads down, its not much proof that they aint got eyes.
Someone noticed they ripped it of Starship Troopers, they have their eyes quite well hidden and it isnt something you notice... Except when you come close and decide to shoot them out
It's was already stated in some interview (I think the PC Gamer preview) that the ant lions react to scent and will attack anything that doesn't smell friendly. This is why the pheromone is so important. Duh.