I was originally going to have the ants go back to the anthill on their own, like in Pikmin. But I didn't really feel like I had the time to make a proper pathfinding system, so I just decided to have them follow you. The ants can move quite fast when you put extra ants on the item they're carrying (even if the item has a weight of 5 you can keep putting more on to make them go faster), but I agree that it still is quite tedious.
Also, if you get all of the food you fight the boss at the end (if you didn't know).