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Collective Behavior of Active Matter: The Curious Case of Fire Ant Rafts

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Thursday, April 21, 2022, 4 pm

This is a past event.

ME-EM Graduate Seminar Speaker Series

proudly presents

Franck J. Vernerey, PhD

University of Colorado, Boulder


When exposed to water, colonies of fire ants (Solenopsis invicta) are well-documented to form buoyant rafts that helps them escape from floods. In this presentation, I will discuss the collective morphogenesis of these rafts when docked to stationary, vertical rods. These living structures consist of a condensed, floating, structural network of interconnected ants on top of which a population of dispersed ants can actively walk. Under these conditions, ant rafts can change their shape substantially and continuously over the span of several hours through a mechanism we call treadmilling. During this process, rafts frequently sprout tether-like protrusions from their edges that fire ants can use to dynamically explore their environment and create land bridges as an escape route. Employing both experimental characterization and an agent-based numerical model, we here unveil a local set of mechanisms that reproduce the stochastic emergence of these instabilities in the absence of long-range interactions, targeted cues, or external gradients. Furthermore, we demonstrate that by modulating their activity level, ant collectives can exhibit oscillatory phases of outwards expansion (exploration) and inwards contraction (dormancy). These results suggest that collective morphogenesis in fire ant aggregations is strongly mediated by local interactions at the constituent length scale. We draw analogies with cell mechanics and discuss potential applications to the development of decentralized, autonomous active matter and swarm robotics.


Franck Vernerey is a professor in the Department of Mechanical Engineering at the University of Colorado, Boulder. He received his PhD from Northwestern University in 2006 in the field of theoretical and applied mechanics. His interests are in developing statistical mechanics approaches to understand the emerging response of soft biological and bio-inspired networks based on the physical interactions between their building blocks. This research has applications in the mechanics of polymers, liquid crystal elastomers, soft biological networks, morphogenesis, and growth. Dr. Vernerey is the author of ~100 scientific publications in peer-reviewed journals and book chapters. He is also the recipient of the NSF career award in 2014 and the Presidential Early Career Award for Scientists and Engineers (PECASE) in 2017.

Invited by: Trisha Sain

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