The ant secretion methyl-4-methyl-pyrrole-2-carboxylate - "innocuous, faintly grassy, sulphurous, or fruitlike with a hint of naphtha", "an ichor of extraordinary power for the ants.
"They sweep their antennae back and forth in advance of the head to catch the odorant molecules. When a forager takes a long turn to the left and starts to run away from the track, its left antenna break out of the odor space first and is no longer stimulated by the guiding substance. In a few thousandths of a second, the any perceives the change and pulls back to the right." (p30-31)
Biophilia: The Human Bond with Other Species
E. O. Wilson, Harvard University Press, 1984