Activity-driven changes in the mechanical properties of fire ant aggregations

Area of Science:

• * Biophysics
• * Materials Science
• * Animal Behavior

Background:

• * Fire ant aggregations function as active materials, converting internal energy into mechanical work.
• * The collective behavior of individual ants influences the macroscopic properties of the aggregation.

Purpose of the Study:

• * To investigate the relationship between fire ant aggregation activity and mechanical properties.
• * To understand how cycles of ant activity affect energy storage, dissipation, homogeneity, and force exertion.

Main Methods:

• * Rheology was employed to measure the mechanical properties of the ant aggregation.
• * Direct visualization techniques were used to observe the aggregation's behavior and structure.
• * A kinetic model was developed to explain the observed phenomena.

Main Results:

• * High activity periods correlate with equal energy storage and dissipation, increased homogeneity, and high outward force.
• * Low activity periods result in predominantly elastic behavior, greater heterogeneity, and reduced outward force.
• * The number of active ants was identified as a key factor governing aggregation dynamics.

Conclusions:

• * Fire ant aggregations display dynamic mechanical properties modulated by the activity levels of their constituent ants.
• * The collective behavior of ants creates a tunable active material with varying force output and structural integrity.
• * A simple kinetic model effectively rationalizes the observed activity-dependent mechanical changes.