An aphid is an in-game item that serves as a permanent food source. Once they spawn they will begin searching for a plant to live under, and will anally release honeydew food and, rarely, a blue super food once they have found a clover and removed some of its phloem for a while. They will only produce one piece of food at a time, and that has to be picked up to allow for the aphid to start producing another.
Ants cannot kill aphids, and aphids can not live or produce food underground. They will die when placed underground for too long. No AI ants will pick up aphids if dismissed.