The observation of scanning electron microscope (SEM) on the cuticle of Tumblebug shows that the cuticle is a kind of biocomposite consisting of chitin-fibers and collagen protein matrix. The observation also shows that there are many underpinnings in the cuticle. The underpinnings are also a kind of biological composite consisting of chitin-fiber layers and collagen protein matrixes. More careful observation indicates that the chitin-fiber layers enwrap the core of the underpinnings forming a kind of helicoidal fiber structure. The maximal pull-out force of the helicoidal fiber structure, related to the fracture toughness of the underpinnings, is theoretically and experimentally investigated and compared with that of parallel fiber structure. It shows that the maximal pull-out force of the helicoidal fiber structure is larger than that of the parallel fiber structure, which gives profitable information for the design of man-made high-performance composites and composite structures.