Black soldier fly (Hermetia illucens L.) prepupae (BSFP) are a sustainable protein source, but the use of full-fat prepupal protein powder in extrusion-based three-dimensional food printing is limited by poor structure and flow control. This study developed black soldier fly prepupal protein-based pastes and evaluated the effects of tapioca starch concentration and thermal treatment on rheology, die swell, and printing stability. Pastes were formulated at 80% moisture content using 0.5% gellan gum, tapioca starch at 0, 2.5, or 5%, and corresponding BSFP powder contents of 24.87, 21.98, and 19.09%, respectively. Thermal treatment significantly strengthened the paste structure, increasing the initial storage modulus to 3998.56, 6248.78, and 8891.23 Pa for 0%, 2.5%, and 5% starch, respectively. Steady shear analysis showed shear-thinning behavior, while model-estimated yield stress after heating increased from 363.58 to 636.06 Pa with starch addition. Large-amplitude oscillatory shear and Chebyshev coefficient analysis showed that starch increased nonlinear elastic resistance and strain stiffening. However, 5% starch caused the high die swell ratio of 1.96 and edge roughness of 0.074 mm. The 2.5% starch formulation showed the lowest edge roughness of 0.049 mm and thickness variation of 8.1%, producing the most stable printed structure. Overall, moderate starch addition improved printability by balancing flow, recovery, and shape retention.