Ant foundress associations are an example of cooperation among non-kin. Across a dozen genera, queens able to found a colony alone often join unrelated queens, thereby enhancing worker production and colony survivorship. The benefits of joining other queens vary with group size and ecological conditions. However, after the first workers mature, the queens fight until only one survives. The presence of cofoundresses, and their relative fighting ability, also affects the extent of cooperative investment before worker emergence. This reveals previously overlooked early conflicts among queens, which reduce the mutualistic benefits of cooperation.