This study used scanning electron microscopy (SEM) to observe the internal structure of forewings from adult male Allomyrina dichotoma. The images showed that the Allomyrina dichotoma forewing is a composite sandwich structure composed of upper and lower stressed skins, a hollow core layer and an abdominal-wall layer. The core layer has an irregular honeycomb-like structure with columellae; the chitin fibers on the surfaces of these columellae are connected to the upper and lower stressed skins. The structure of corrugated steel web (CSW) bridges is similar to that of a beetle forewing: the top and bottom concrete plates are similar to the upper and lower stressed skins, whereas the CSWs are similar to the irregular thin-walled core layers. In engineering applications, CSWs are prone to buckling. However, beetle forewings have a lightweight, high-strength composite structure that can adapt to complex, variable natural environments and external loads without breaking due to the reinforced columellae inside the structure. Hence, this work studied the microstructure of beetle forewing in an attempt to design a CSW with a columellar structure similar to that found in the core layer of the forewing. Moreover, a finite element model was used to quantitatively analyze the effects of the columellae on the deformation, shear stress distribution and buckling stability of CSW bridges, which can provide a reference for the bionic structure of a beetle forewing and for the optimization of CSW bridges.