As far as I have seen, the vast majority of workers in colonies of diurnal, non-nomadic species return to their nests and remain there at night. The colonies seem to forage largely during the day. However, a few individuals of said colonies would still wander far from the nest at night. I don’t believe they are lost because they still seem to be following pheromone tracks.
Why do they do that? What drives them to still come out at night and not remain in the nest like most other workers do? Are they any different in terms of caste? Are they always the same individuals? Is there a selection process to decide who will wander off at night? Are they somehow invalid and can't tell day from night? Is that somehow evolutionarily advantageous (e.g. having a few workers take some risk at night, maintaining the pheromone tracks throughout the night so that the other workers don't have to start all over the next morning)?
Someone (jokingly) told me those ants must still be hungry, but I don't immediately buy that explanation because my understanding is that most species will store food in the nest in one form or another anyway, or they just share food by trophollaxis.