In this project the PIs will use laboratory experiments and simulations to systematically study how the behavioral and physical interactions of fire ants (Solenopsis invicta) with cohesive granular media influence the formation of underground nests. The specific objectives are: (1) To study how ant colonies build and respond to perturbations in different media. (2) To understand how ground properties affect nest structure and stability. (3) To study multi-agent simulation models of nest formation. A major problem in modeling nest construction is that the physics of cohesive soils is not sufficiently developed to predict stability of structures. To address this question the PIs will combine information from the first two aims into a multi-agent simulation to model nest formation; individual behavioral rules will be derived from observations and cohesive soil rule will be derived from physics studies. These will be integrated to form a minimal physical model using granular physics simulation and ant grain interaction that captures the observed nest formation and allows the testing of different hypotheses of colony function. The PIs will coordinate with high schools serving populations underrepresented in the sciences to recruit teachers into the research labs and place graduate students into local high schools as teaching assistants. In addition they will also institute engineering-science team projects for undergraduates so that students gain a better understanding of interdisciplinary research at the intersection of biology and physics. The proposed experiments and models can aid in controlling invasive species such as S. invicta by learning how soil modification affects nest building. The multi-agent simulations will be of use to many outside this field for solving scientific or engineering problems. In addition this research program will provide a platform for modeling bioturbation, a major factoring affecting planetary ecology.
. PI: Daniel I. Goldman, School of Physics, Georgia Institute of Technology, Atlanta, GA, co-PI: Michael A. D. Goodisman, School of Biology, Georgia Institute of Technology, Atlanta, GA Social insects, such as ants, termites, social bees, and social wasps, live in colonies composed of interacting individuals that work together to complete complex tasks. Social insect colonies have justifiably been called "superorganisms" because of the tremendous integrative nature of their societies. The evolution of sociality in insects relied critically on the presence of nests. Nests help insects to survive, reproduce and develop young. The construction of nests by social insects is critical for survival and represents a major achievement. For example, some termites build nests that extend up to eight meters in height and persist for decades. These giant nests are all the more remarkable because the termites that build them are blind and less than one centimeter in length. Thus the construction of termite nests is equivalent to humans constructing houses the size of small mountains in the dark and without the aid of technology. The seemingly impossible task of nest building can be completed because social insects employ a concept of so called ‘self organization’ during nest construction, which is totally different from the humans do. This implies formation of sophisticated and adaptive higher-level nest patterns that emerge from simple, lower-level interactions. Thus further understanding of the intricacies and dynamics of nest construction requires detailed investigations of how the physics of construction materials affect nest building, structure, and function. The red imported fire ant, Solenopsis invicta, is a good candidate for studying nest building in real materials and collective intelligence of complex social systems. S. invicta are the invasive widely spread species in the Southern Unites States and their basic biology has been very well studied. It is known that fire ants build nests in almost any type of soil. These soils differ in particle size and wetness. Consequently, the social behavior and strategies of S. invicta upon construction and excavation can be tested over a wide range of substrates and provide a greater understanding of how biological organisms interact and adapt to complex environments. The objective of this research is to investigate how the behavioral rules and physical materials that S. invicta fire ants use to construct nests influence each other and affect nest structure and function. We combine expertise in social biology, granular media physics and nonlinear dynamics of collective behavior to investigate the rules by which ants interact with each other and with complex media. During this grant we have discovered biomechanical principles of movement in confined environments, developed systems to monitor the time evolution of two (using "ant farms") and three dimensional (using custom CT scanning) nests in the laboratory, studied ant inspired entangled granular media, discovered principles of soil collection, and learned about social organization of collective digging. We have trained three graduate students, one postdoctoral researcher, approximately eight undergraduates, and two high school interns. Our work has been featured in the popular press.
