Most structural materials existing in nature take the form of composite. After centuries’ evolution and modification, these natural materials gain highly optimized structures and prominent performances. The SEM observation on the cuticle of Hydrophilidae shows that the cuticle is a biocomposite reinforced with chitin fibers. The chitin fibers are embedded in a protein matrix of the cuticle in the form of layers. A kind of revolving fiber layup was found. Observation also shows that there is a kind of special branched fiber consisting of a long fiber and many short fibers. The maximum pullout force of the branched fiber is analyzed. The results show that the maximum pullout force of the branched fiber is distinctly larger than that of ordinary straight fiber.