In peer-to-peer file sharing systems, file replication helps to avoid overloading file owners and improve file query efficiency. Aiming to achieve high replica utilization and efficient file query with low overhead, this paper presents a file replication mechanism based on swarm intelligence, namely SWARM. Recognizing the power of collective behaviors, SWARM identifies node swarms with common node interests and close proximity. It determines the location of a file replica based on the accumulated query rates of nodes in a swarm. Replicas are shared by the nodes in a swarm, leading to less replicas and high query efficiency. Simulation results demonstrate the efficiency and effectiveness of the SWARM mechanism in comparison with other file replication methods.