Behavioural biomechanics: leaf-cutter ant cutting behaviour depends on leaf edge geometry

Area of Science:

• Ethology
• Biomechanics
• Insect behavior

Background:

• Leaf-cutter ants cultivate symbiotic fungi using freshly cut leaves.
• Ants typically use a knife-cutting strategy with one mandible.
• Alternative scissor-cutting behavior is observed at leaf edges.

Purpose of the Study:

• Investigate leaf-cutter ant cutting strategy preferences based on leaf edge geometry.
• Determine the mechanical basis for the observed behavioral shift between cutting strategies.

Main Methods:

• Conducted in vivo behavioral assays to observe ant cutting preferences.
• Performed ex vivo cutting experiments to analyze mechanical forces.
• Varied leaf edge geometry (straight, wide notches, narrow notches) in experiments.

Main Results:

• Ants preferred scissor-cutting on straight or wide-notched edges.
• Knife-cutting was preferred on narrow-notched edges.
• Knife-cutting on wide notches required high forces due to leaf buckling and bending, with many mandibles failing to initiate cuts.

Conclusions:

• Leaf edge geometry dictates the preferred cutting strategy in leaf-cutter ants.
• Scissor-cutting may be an adaptation to overcome mechanical challenges (buckling, bending) of thin leaves during knife-cutting.
• The findings highlight the interplay between morphology, behavior, and mechanics in insect foraging.