Attraction, Dynamics, and Phase Transitions in Fire Ant Tower-Building

Nave, Gary K.; Mitchell, Nelson T.; Dick, Jordan A. Chan; Schuessler, Tyler; Lagarrigue, Joaquin A.; Peleg, Orit

doi:10.3389/frobt.2020.00025

Cited by 7 publications

(2 citation statements)

References 61 publications

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“…structures such as towers nucleated about substrates [20]. While the behaviour and flow of 3D ant towers has been examined [20,21], questions remain regarding the long-term dynamics of approximately two-dimensional (2D) rafts. Mlot et al [11] reported that, upon being placed into the water as approximately 3D spheroids, ant rafts spread out rapidly.…”

Section: Introductionmentioning

confidence: 99%

Treadmilling and dynamic protrusions in fire ant rafts

Wagner

Such

Hobbs

et al. 2021

J. R. Soc. Interface.

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Fire ants ( Solenopsis invicta ) are exemplary for their formation of cohered, buoyant and dynamic structures composed entirely of their own bodies when exposed to flooded environments. Here, we observe tether-like protrusions that emerge from aggregated fire ant rafts when docked to stationary, vertical rods. Ant rafts comprise a floating, structural network of interconnected ants on which a layer of freely active ants walk. We show here that sustained shape evolution is permitted by the competing mechanisms of perpetual raft contraction aided by the transition of bulk structural ants to the free active layer and outward raft expansion owing to the deposition of free ants into the structural network at the edges, culminating in global treadmilling. Furthermore, we see that protrusions emerge as a result of asymmetries in the edge deposition rate of free ants. Employing both experimental characterization and a model for self-propelled particles in strong confinement, we interpret that these asymmetries are likely to occur stochastically owing to wall accumulation effects and directional motion of active ants when strongly confined by the protrusions' relatively narrow boundaries. Together, these effects may realize the cooperative, yet spontaneous formation of protrusions that fire ants sometimes use for functional exploration and to escape flooded environments.

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Section: Introductionmentioning

confidence: 99%

Treadmilling and dynamic protrusions in fire ant rafts

Wagner

Such

Hobbs

et al. 2021

J. R. Soc. Interface.

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“…Free boundary problems arise in other natural processes, including, but not limited to, dendritic crystal growth [30,31] and flame front propagation [32][33][34]. Continua may also be used to model other collective behaviours [4,35,36] such as fish schooling [37], bird flocking [38], bat swarming [39,40] and ant colony formation [41,42].…”

Section: Introductionmentioning

confidence: 99%

Penguin Huddling: A Continuum Model

Harris

McDonald

2023

Acta Appl Math

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Penguins huddling in a cold wind are represented by a two-dimensional, continuum model. The huddle boundary evolves due to heat loss to the huddle exterior and through the reorganisation of penguins as they seek to regulate their heat production within the huddle. These two heat transfer mechanisms, along with area, or penguin number, conservation, gives a free boundary problem whose dynamics depend on both the dynamics interior and exterior to the huddle. Assuming the huddle shape evolves slowly compared to the advective timescale of the exterior wind, the interior temperature is governed by a Poisson equation and the exterior temperature by the steady advection-diffusion equation. The exterior, advective wind velocity is the gradient of a harmonic, scalar field. The conformal invariance of the exterior governing equations is used to convert the system to a Polubarinova-Galin type equation, with forcing depending on both the interior and exterior temperature gradients at the huddle boundary. The interior Poisson equation is not conformally invariant, so the interior temperature gradient is found numerically using a combined adaptive Antoulas-Anderson and least squares algorithm. The results show that, irrespective of the starting shape, penguin huddles evolve into an egg-like steady shape. This shape is dependent on the wind strength, parameterised by the Péclet number Pe, and a parameter $\beta $ β which effectively measures the strength of the interior self-generation of heat by the penguins. The numerical method developed is applicable to a further five free boundary problems.

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Catch bond kinetics are instrumental to cohesion of fire ant rafts under load

Wagner,

Lamont,

White

et al. 2024

Proc. Natl. Acad. Sci. U.S.A.

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Dynamic networks composed of constituents that break and reform bonds reversibly are ubiquitous in nature owing to their modular architectures that enable functions like energy dissipation, self-healing, and even activity. While bond breaking depends only on the current configuration of attachment in these networks, reattachment depends also on the proximity of constituents. Therefore, dynamic networks composed of macroscale constituents (not benefited by the secondary interactions cohering analogous networks composed of molecular-scale constituents) must rely on primary bonds for cohesion and self-repair. Toward understanding how such macroscale networks might adaptively achieve this, we explore the uniaxial tensile response of 2D rafts composed of interlinked fire ants ( S. invicta ). Through experiments and discrete numerical modeling, we find that ant rafts adaptively stabilize their bonded ant-to-ant interactions in response to tensile strains, indicating catch bond dynamics. Consequently, low-strain rates that should theoretically induce creep mechanics of these rafts instead induce elastic-like response. Our results suggest that this force-stabilization delays dissolution of the rafts and improves toughness. Nevertheless, above 35 % strain low cohesion and stress localization cause nucleation and growth of voids whose coalescence patterns result from force-stabilization. These voids mitigate structural repair until initial raft densities are restored and ants can reconnect across defects. However mechanical recovery of ant rafts during cyclic loading suggests that—even upon reinstatement of initial densities—ants exhibit slower repair kinetics if they were recently loaded at faster strain rates. These results exemplify fire ants’ status as active agents capable of memory-driven, stimuli-response for potential inspiration of adaptive structural materials.

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Attraction, Dynamics, and Phase Transitions in Fire Ant Tower-Building

Cited by 7 publications

References 61 publications

Treadmilling and dynamic protrusions in fire ant rafts

Treadmilling and dynamic protrusions in fire ant rafts

Penguin Huddling: A Continuum Model

Catch bond kinetics are instrumental to cohesion of fire ant rafts under load

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