Spiders and silkworms employ the complex flow of highly concentrated silk solution as part of silk fiber spinning. To understand the role of fluidic forces in this process, the flow of silk solution in the spider major ampullate and silkworm silk glands was investigated using numerical simulation. Our simulations demonstrate significant differences between flow in the spider and silkworm silk glands. In particular, shear flow effects are shown to be much greater in the spider than the silkworm, the silkworm gland exhibits a much different flow extension profile than the spider gland, and the residence time within the spider gland is eight times greater than in the silkworm gland. Lastly, simulations on the effect of spinning speed on the flow of silk solution suggest that a critical extension rate is the initiating factor for fiber formation from silk solution. These results provide new insight into silk spinning processes and will guide the future development of novel fiber spinning technologies.