If you are looking for a (e.g., LitRPG, Horror, or Classic), let me know so I can point you to the exact "Swarm" book and the best site to download it for free. Rob Roy — Complete by Walter Scott - Project Gutenberg
A human scientist, Dr. Simon Afriel, travels to a distant asteroid colony inhabited by an ancient, mindless alien collective known as the Swarm . He intends to steal their genetic secrets to help humanity genetically engineer their own labor force. He believes the Swarm is unintelligent and easily manipulated.
Humans live underground on Astire, mining minerals for immortality. Suddenly, communication with remote settlements is cut off. Teams sent to investigate disappear without a trace. The protagonists eventually realize they are facing a biological threat—a "Swarm"—unlike anything humanity has ever seen.