[Aim]  To reveal the mechanisms underlying the morphological changes involved in the excavation behavior of scarab beetles (Scarabaeoidea), and examine how these relate to the evolution of functional morphology associated with digging behavior in this taxon. [Methods]  Eight scarab species with differing excavation abilities were selected. Micro- computer tomography (micro-CT), was used to scan and construct 3D models of the pronotum and the main internal muscles involved in forecoxal movement (the tergal remotor and tergal promotor), in these species. External differences in pronotum shape were examined using 3D geometric morphometrics, whereas internal structures were compared quantitatively by assessing their muscle volume, cross-sectional area, and attachment surface area. [Results]  Principal component analysis identified notable differences in the shape of the pronotum between strong and weak excavators. The pronotum of strong excavators has a more pronounced “saddle-shaped” arch and a more streamlined “wedge-shaped” profile, which probably aid in stress relief and increase stability. Quantitative muscle assessments revealed that the attachment area ratio of the tergal remotor muscle was significantly larger in species with stronger excavating ability (P<0.01). However, no significant differences were observed in the mid-cross-sectional area, volume, or other related measures, of this muscle (P>0.05).  [Conclusion]  Scarab beetles’ prothoracic structures reflect evolution for different levels of excavating ability. In species with strong excavating ability, the external pronotum has become more arched and streamlined to boost mechanical stability, while internally, increased muscle attachment areas create a stronger anchor and improve muscular efficiency, without overtly increasing muscle size. This study highlights the advantages of multidimensional quantitative morphology in functional morphology research, and offers a clear example of how biological structures adapt to different environmental requirements.