Environmental Adaptations in Fire Ant Mound Construction

Fire ants are highly invasive and robust social insects that thrive in diverse environments well beyond their native range. Colonies build elaborate subsurface nests by removing soil pellets that are deposited above ground. A surface mound with complex internal structures is eventually formed, although its construction and function are not well understood. We hypothesize that fire ants' success is linked to above- and below-ground architectural adaptations across environmental conditions. To begin to investigate how soil moisture and temperature influence nest structures, we focus on incipient mound formation in the lab. Using a custom-built surface scanner, we acquire high-resolution, time-resolved 3D height maps during the first 24 hours of construction in naturalistic soil. We find that surface features are qualitatively different across soil moisture contents: in wetter soil, ants build many tall and narrow vertical towers sometimes connected by bridges, whereas in drier soil, ants build a few broad, shallow heaps. Surface features are similar across temperatures, though construction rates tend to be higher in warmer conditions. Our results demonstrate that environmental factors influence mound construction, and future work will investigate the origins of this environmentally driven structural variation as well as the interplay between substrate physics and collective behavior in mound formation.