Over 3.5 billion years, life has evolved towards ever-greater size and complexity. At critical transitions, this occurred when entities formed collectives (e.g. cells into multicellular bodies, individuals into eusocial societies, species into obligate mutualisms). Towards explaining this trend, I will integrate two emerging perspectives—social evolution and metabolic ecology—using scaling laws to explore energy efficiencies gained as organisms crossed these major transitions. Extending my research on the physiology of fungus-growing ant societies, I will use a metabolic currency to study the evolutionary trend towards ever-larger agricultural systems. Ants (tribe Attini) began cultivating fungi 50 million ago and have since evolved into over 230 species common across the new world tropics. My research has suggested that these farming ant societies, like those of humans, face efficiency constraints related to metabolism. I found that species with larger colony-farms tend to become increasingly efficient, producing larger fungus crops while losing relatively less energy to metabolic respiration. I will extend advanced techniques I pioneered, using a cutting edge respirometry system to link performance and operational size at each level of organization, from newly-mated queens that found colonies, to societies of sterile workers cultivating fungus, and then whole colony-farms that use public health strategies to protect fungal symbionts. Decades of research by my host, Prof. Boomsma, have made fungus-growing ants a model system in biology, rivaling the honeybee, and I will use this system to ask fundamental integrative questions in biology. I will also transfer knowledge by organizing and teaching three courses—a respirometry course (2014) and a tropical field course in Panama (2013 & 2015). A return phase with Prof. Rob Dunn (USA) will cement international collaboration and enable high impact outreach in Europe, building on his massive citizen-science infrastructure.