Engagement of gear-like structures on mandibles of D. hercules during opening and closing; engaged regions of mandibles were exposed using a file. A Lateral view of the head from the left side; dotted lines indicate the position of the transverse section B interior view of the head from the ventral side C diagram of the engagement region; gear-like structures are emphasized by stipple. Abbreviations: R = right compound eye; L = left compound eye. Scale bar: 7 mm.