Janssen effect in columns of fire ants

Area of Science:

• Physics of granular materials
• Collective behavior in biological systems
• Biophysics

Background:

• Granular columns, both passive (grains) and active (e.g., ants), exhibit unique load-bearing properties.
• The Janssen effect describes how pressure in passive granular columns saturates with depth.
• Understanding active granular systems is crucial for bridging physics and biology.

Purpose of the Study:

• To investigate the force-chain structures and load-bearing capacity in fire-ant columns.
• To compare the behavior of active ant columns with passive granular columns.
• To model the influence of ant activity on structural integrity and pressure fluctuations.

Main Methods:

• Experimental study of fire-ant columns under varying mass loads.
• Analysis of force-chain development and pressure distribution at the column base.
• Computational simulations incorporating friction, wall interactions, and fluctuating active forces.

Main Results:

• Fire-ant columns develop force-chain structures, supporting weight in a Janssen-like manner.
• Activity-induced rearrangements alter force-chain structures, reducing support over time.
• Pressure fluctuations at the column base exhibit scaling consistent with the law of large numbers.

Conclusions:

• Active ant columns exhibit emergent structural properties analogous to passive granular systems.
• Ant activity introduces dynamic changes to force-chain stability and pressure distribution.
• Simulations effectively capture experimental observations, highlighting the role of fluctuating forces.