Comparative morphology and mechanics of the predatory foreleg of praying mantis species (Mantodea)

Praying mantises (Mantodea) are a relatively small but diverse order of insects. They all share a crucial characteristic: they are all predators that use their forelegs to capture prey. This common task is accomplished by a variety of ecomorphs specialized for a substrate (grasses, soil, bark, etc.), hunting strategy (ambush vs pursuit), or mode of movement (climbing vs running). Here, we describe the morphological variation among forelegs, and compare the biomechanical properties across the phylogeny of mantis species. We have adapted a machine-learning algorithm (DeepLabCut) to identify 24 landmarks on the femur and tibia of over 500 species of mantises. We describe the variability of the shape space across the phylogeny, and identify subgroups with extreme forms. Using a geometric relationship between the shape of the foreleg and the optimal size of prey, we find that the majority of species occupies a narrow range in this space. A small number of species with adaptations for camouflage are limited to smaller prey, and a larger group that specialize in pursuing prey on a flat substrate can capture larger prey. We then use micro-CT to capture the internal morphology of the foreleg in a subset of species, particularly the volume of flexor muscle and the arrangement of the tendon. These are used to construct a biomechanical model of the closing force these species can generate.