Evolution of brain size in class-based societies of fungus-growing ants (Attini)

► We examined sociality and brain size in nine genera of fungus-growing ants (Attini). ► Fungus-growing ants showed broad variation in colony size and social organization. ► Brain size varied among taxa in larger colonies and in more tightly knit societies. ► Larger colony size was associated with differential investment in olfactory brain centres. ► Analyses of social complexity using a scalogram yielded results similar to those using group size as a proxy.