In this study, the microstructures of Rutelidae cuticle, a natural biocomposite, were observed with scanning electronic microscope (SEM). It was found that the insect cuticle has a laminated microstructure consisting of chitin fiber and protein matrix. There are particular spiry layups in the cuticle. The maximal pull-out force of the spiry layup is analyzed and compared with that of conventional 0degrees-layup based on their representative models. The result shows that the pull-out force of the spiry layup is markedly larger than that of the conventional 0degrees-layup. The corresponding experiment on the maximal pull-out forces of both spiry layup and the 0degrees-layup is conducted, and it shows that the maximal pull-out force of the spiry layup is markedly larger than that of the 0degrees-layup, which verifies and demonstrates the validity of the presented model. (C) 2004 Elsevier B.V. All rights reserved.