Meeting Abstract
Leaf-cutter ants are the prime consumers of plant material, and key pest species throughout the Neotropics. A mature colony may cut thousands of square meters of leaf area per year, deploying foraging parties which consist of differently-sized workers performing distinct tasks: smaller ants tend to cut tender leaves, while larger ants harvest tougher leaves. This ‘division of labour’ is believed to provide the colony access to a larger variety of food sources, and hence increase its fitness and resilience. The ability of a worker to cut a given food source is constraint by the available bite force, and understanding how bite forces vary with size is hence crucial for further assessing this hypothesis. We measured bite forces for Atta vollenweideri workers across the entire size-range, covering approximately one order of magnitude in body mass. Bite forces were measured with a custom-built force rig based on force-sensitive capacitors connected to adjustable cantilevers, which allowed us to control the gap width and hence the mandibular opening angle. Even after accounting for the effects of size expected from isometry, large workers produced significantly higher forces than small workers. This positive allometry originates from (I) disproportionally larger head capsules accommodating greater mandible closer muscles and (II) a systematic increase in the mechanical advantage. Bite forces of larger ants are comparable to those of considerably heavier cockroaches, underlining the adaptation of leaf-cutter ants to produce the high forces required to overcome the mechanical resistance of their food sources. Our results indicate that large ants are particularly well-suited for cutting tough leaves, but why are tender leaves mainly cut by smaller ants? We speculate that this behaviour is explained by the ergonomics of cutting, which will be investigated in future studies.
