Leaf-cutter ants serve as keystone species that affect and advance diversity, productivity, and nutrient flow in tropical habitats. Field work was conducted in Costa Rica between May and June 2017 to investigate the role of environmental factors on biomass transport by leaf-cutter ants. Thirty leaf-cutter ant trails were identified along hiking paths throughout La Selva Biological Station, and measures corresponding to foraging efficiency (i.e. speed of biomass transport, average mass of forage transported, trail workforce composition, and biomass transport rate) were documented, along with potential environmental determinants of foraging efficiency (e.g. time of day, precipitation, canopy cover, proximity to forage source and colony). Multiple linear regression models indicated that time of day was significantly associated with workforce composition, weight of forage transported, speed of transport, and biomass transport rate. Precipitation was associated with workforce composition, weight of forage transported, and biomass transport rate. Substrate type was associated with speed of transport and biomass transport rate. Forage source proximity was associated with workforce composition, while proximity to colony was associated with weight of forage transported. Biomass transport rate was also associated with canopy cover. This study characterizes key features of the foraging ecology of leaf-cutter ants, and demonstrates how foraging efficiency is affected by environmental factors.