Morphology and material composition of raptorial foreleg cuticles in praying mantises Gongylus gongylodes and Sphodromantis lineola.

Praying mantises (Mantodea, Insecta) are capable of capturing larger invertebrates and also smaller vertebrates with their raptorial forelegs. Forelegs may exhibit morphological adaptations based on the type of prey they prefer (e.g., softer or harder invertebrates). Since the functionality of a structure is also influenced by its material composition, it could be tailored to match the prey as well. To pave the way for deeper studies on trophic adaptations in insects, this study investigates the morphology, material composition and mechanical properties of the raptorial forelegs of two species of praying mantises with different prey preferences. Sphodromantis lineola favours harder and larger invertebrates, such as cockroaches (Blattaria), whereas Gongylus gongylodes feeds on softer and smaller invertebrates like flies (Diptera). Both males and females were examined in both species to assess potential sexual dimorphism. The results suggest that the morphology of the raptorial forelegs, the arrangement and tiltability of the spines, and the material mechanical properties of the leg cuticle could potentially be related to the preferred prey type. Autofluorescence documentations reflected the presence of micro gradients in the spines, which are related to their mechanical properties. However, pigmentation in the structures of G. gongylodes seemed to corrupt the autofluorescence, complicating comparisons between the species. Elemental analysis confirmed the presence of traces of transition and alkaline earth metals in the raptorial forelegs, though no significant species-specific differences and no correlations to the mechanical properties were detected.