How would one go about marking one or more ants in a nest so as to least disturb the ant and the nest? The goal is to be able to know which ant you marked months, or many years up to a lifespan later, while at the same time have the least influence of the markings on the behavior of the ant and the interaction between the marked and not-marked ants.
For this purpose, people usually paint ants on top of the thorax (not on the head where it can prevent eyes and antenna to function normally, nor on the abdomen where it can block the spiracles and prevent respiration), with a bit of acrylic paint applied with a toothpick. Combination of colors are used to identify individuals.
These techniques are currently being replaced by the use of RFID tags and Flashcodes in science, to automate recordings.