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Mandibles in insects are “multi-purpose” tools: they are used for cutting, masticating, digging, material transport, prey capture and defense. In contrast to this functional complexity, the kinematics of most insect mandibles are typically characterised by a simple hinge joint. Such characterisations are often based on morphological data, but without quantitative kinematic analysis.
We developed a recording setup and kinematic analysis pipeline to rigorously test this “hinge joint hypothesis” (see figure). So far, we extracted the kinematics of Atta vollenweideri leaf-cutter ant mandibles. At large opening angles, mandibles mostly yawed, in accordance with a hinge motion. But at small opening angles, mandibles yawed and pitched, suggesting a second degree of freedom in rotation. For more information, see our recent preprint: https://www.biorxiv.org/content/10.1101/2023.08.28.555128v1.full
How do different surfaces influence the adhesive performance of insects?
On rough surfaces such as rocks or tree bark for example, insects can employ not only their pads but also their claws to help them adhere. What role does surface chemistry play in the pad-surface interaction?Variations in surface chemistry lead to differences in the ability of contacting liquids to spread, surface wettability. If the liquid secreted from the pads and mediating their contact to surfaces plays a role in adhesion (wet adhesion model), we would expect the measured adhesive forces to be a function of the surface wettability.
To test this hypothesis, we produced smooth surfaces of varying wettability by Chemical Vapour Deposition (CVD), characterised them by goniometry and Atomic Force Microscopy, and performed single pad adhesion force measurements using a custom-made fibre-optic force sensor.
How do insects continue to stick to surfaces even as they get larger and heavier?
Their footpads do not grow disproportionately large to increase their contact area, but they do become more efficient. What is the source of their enhanced efficiency? We explore the hypothesis that the liquid secreted by the insect pads at their contact zone is responsible for them clinging on.
We test whether the surface tension and viscosity of the secretion vary systematically with size by performing paired Interference Reflection Microscopy and dewetting measurements on individuals spanning almost 3 orders of magnitude in mass. Learning how natural adhesive organs overcome stress concentrations and scaling issues to maintain their attachment can then inform the next generation of artificial adhesives.
Insects parade an impressive diversity of morphologies, colours, and sizes.
One factor of their success are their exceptional locomotion abilities: they run, climb, carry loads, jump, fly or strike – all by fine-tuning mechanical and kinematic constraints. Understanding the mechanical constraints which govern the kinematics and dynamics observed during different locomotor tasks will not only extend our knowledge of insect locomotion but may ultimately also improve the operational fitness of six-legged robots deployed in demanding environments.
To address these challenges, we developed a variety of different setups like rotational platforms with exchangeable walking substrates or various insect treadmills to record the locomotion of our insects. We film them with multiple cameras and track points of interest using markerless pose estimation. By combining the different viewports, we can reconstruct the locomotion and analyse it in 3D using established workflows.
To cut vegetation, leaf-cutter ants need large bite forces produced by strong mandible muscles. In invertebrates, these muscles cannot be packed outside the skeleton, instead, their size is constrained by an outer exoskeleton. So, how do these small insects (most leaf-cutters are only a few mg) manage to produce forces large enough to cut tough leaves?
We approach this question in several ways: First, we measure bite forces of foraging ants. These forces in relation to the mandibular cutting forces determine the ability to cut a given material. Second, we take a closer look inside the head capsule using micro-computed tomography and quantify the size and geometry of the muscle and lever system. We use custom-written algorithms to trace up to several thousand individual muscle fibres per ant and muscle! Third, we develop predictive models enabling us to directly link size and shape of the insect bite apparatus to bite forces and cutting ability.