Cretaceous stick insects had enlarged defensive hind legs

Two species of stick insect from the Early Cretaceous Jehol Biota of China had enlarged hind femora that are significantly larger than those of other known members of their family, indicating that the modified legs served an active defensive function. The approximately 125-million-year-old fossils, Coniphasma inflatum sp. nov. and Coniphasma breve sp. nov., are described in BMC Biology . The two species combined several conspicuous features.

Both possessed irregular color markings on well-developed wings, and their enlarged femora aided in camouflage. Their legs also carried prominent longitudinal carinae, or raised ridges, bearing rows of denticulate notches. According to the researchers, these structures enhanced the active defensive strategy the insects could employ after camouflage had failed.

Relative size distinguishes the hind femora of Coniphasma inflatum and C. breve from those of other known species in Susumaniidae. Their enlargement, together with the notched ridges on the legs, supports the interpretation that the legs functioned as active defensive weapons rather than representing only the visual resemblance associated with stick insects. The finding is based on fossil morphology from two species; it does not reveal how widespread active defensive behavior was across the wider stick insect group.

The authors conclude that the origin of enlarged hind femora probably predates wing regression in Phasmatodea. Both Jehol species retained well-developed wings while also possessing the enlarged femora interpreted as defensive structures. The discovery also indicates that many of the highly diverse morphological traits seen in living stick insects were already established during the Mesozoic.

Moreover, the researchers suggest that these features evolved independently multiple times within Phasmatodea.

Subject of Research: Fossil evidence of active defense in Early Cretaceous stick insects

Article Title: Enlarged hind femora as active defensive weapons in Cretaceous stick insects

Article References: Zhao, X., Ren, D., Yang, H., & Gao, T. (2026). Enlarged hind femora as active defensive weapons in Cretaceous stick insects. BMC Biology. https://doi.org/10.1186/s12915-026-02765-7

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02765-7

Keywords: Cretaceous, stick insects, Phasmatodea, hind femora, active defense, fossil morphology, Jehol Biota, wing regression, insect evolution, Susumaniidae, Enlarged, hind