Raptorial insects evolved independently across multiple lineages

A research group including Professor Yasuoki Takami and Graduate Student Hikaru Miyaji (at the time of research) at the Graduate School of Human Development and Environment, Kobe University, Curator Tadashi Shinohara at the Ishikawa Insect Museum, and Researcher Akihiro Hirayama at the Hyogo Prefectural Institute of Technology, clarified that specialized forelegs (raptorial legs) for capturing prey such as seen in praying mantises did not evolve into the same shape despite fulfilling the same function of predation. Contributions to understanding biodiversity are expected. The findings were published in Scientific Reports on July 7.

In insects, predatory forelegs (raptorial legs) evolved independently at least 7 times across different groups. Raptorial legs possess structures and functions pinching prey between the femur and tibia (3rd and 4th segments of legs). Because these are common between different groups, shapes appear identical at first glance.

On the other hand, research investigating how similar these are based on evolutionary perspectives did not exist. The group targeted 6 groups of insects possessing raptorial legs and measured the lengths of each segment of the forelegs of insect with raptorial legs, comparing evolution of shapes by regarding forelegs (not raptorial legs) of closely related groups as ancestral states. In addition, middle and hind legs lacking the raptorial structure, alongside the shape of the head and prothoraxes in predatory species, were similarly compared.

As a result, it was revealed that raptorial legs of each group possess distinct shapes respectively. In the process of evolution from normal forelegs to raptorial legs, moderate similarities were found in directions of shape evolution. On the other hand, convergent evolution, where groups evolve to take on more similar shapes, had not occurred. In shapes of middle legs and hind legs, common evolutionary trends between groups were not observed. Furthermore, it was also found that shapes of raptorial legs of aquatic groups such as giant water bugs and water scorpions were heterogeneous.

Across all groups, the researchers also found that the evolution of raptorial forelegs was accompanied by a broader head and a longer, more slender prothorax. Correspondence relationships between function and shape being "one-to-many" are considered to connect to diverse evolution.

Takami said, "Did everyone know that raptorial forelegs like praying mantises evolved repeatedly at least 7 times from ancestors possessing normal forelegs? Among those, 6 times can be investigated by collecting species present in Japan. Students proficient at insect collecting went out to collect them, or borrowed specimens from fellow researchers, enabling us to measure those shapes. Even familiar insects possess mysterious and interesting shapes when looking closely. Through measuring such shapes, we wish to unravel mysteries of functions and evolution that shapes possess."

Journal Information
Publication: Scientific Reports
Title: Quantifying the repeated evolution of insect raptorial forelegs
DOI: 10.1038/s41598-026-57616-w