Ants hold a grudge: Associative learning of non-nestmate cues improves enemy recognition

Recognition protects biological systems of all scales, from cells to societies. Social insects recognize their nestmates by colony-specific chemical labels, which individuals store as “templates” in their memories. The distributed model of nestmate recognition predicts that individual experiences cause variation between the recognition templates that different individuals store in their memory. Here, we show for the first time that ants associatively learn recognition labels of both friends and enemies during brief encounters. Because different individuals will accumulate different experiences throughout their lives, their later decisions on whether to accept or reject other individuals will also vary. Individual associative learning can thus explain many phenomena from nasty neighbour effects to age polyethism. To avoid chaos caused by inconsistent decisions across individuals, decisions are made in a distributed manner at the colony level. Group-level decision can thus be much more accurate than any individual decision alone.