A general biomechanical model for the relation between bite force and mandibular opening angle in arthropods

Bite forces play a key role in animal ecology: they affect mating behaviour, fighting success, and the ability to mechanically process food. Although feeding habits of arthropods have an enormous ecological and economical impact, we lack fundamental knowledge on how the morphology and physiology of their bite apparatus controls bite performance and its variation with mandible gape. To address this gap, we derived a comprehensive biomechanical model that characterises the relationship between bite force and mandibular opening angle from first principles. We validate the model by comparing its geometric predictions with direct morphological measurements on CT-scans of Atta cephalotes leaf-cutter ant majors. We then demonstrate its deductive and inductive power with four exemplary use cases: First, we extract the physiological properties of the leaf-cutter ant mandible closer muscle from in-vivo bite force measurements, and so add to the few studies on force-length properties of arthropod muscle. Second, we show that leaf-cutter ants are extremely specialised for biting: they generate maximum bite forces equivalent to about 2600 times their average body weight – at least a factor of five in excess of the largest weight-specific forces reported in the literature for any animal. Third, we discuss the relative importance of morphology and physiology in determining the magnitude and variation of bite force, so providing guidance for comparative work. And last, through rational analysis of the model, we suggest a hierarchy of model simplifications and assess the performance of ‘minimum’ models which predict bite force from a reduced set of easily accessible parameters. We hope that our work will facilitate future comparative studies on the insect bite apparatus, and advance our knowledge of the behaviour, ecology and evolution of arthropods.