Swarming agents in networks of preferably physically distributed processing nodes are used for data acquisition, data fusion, and control applications. An architecture for active surveillance systems is presented in which simple mobile agents collectively process real-time data from heterogeneous sources at or near the origin of the data. System requirements are specifically matched to the needs of a surveillance system for the early detection of large-scale bioterrorist attacks on a civilian population, but the same architecture is applicable to a wide range of other domains. The pattern detection and classification processes executed by the proposed system emerge from the coordinated activities of agents of two populations in a shared computational environment. Detector agents draw each other's attention to significant spatio-temporal patterns in the observed data stream. Classifier agents rank the detected patterns according to their respective criterion. The resulting system-level behavior is adaptive, robust, scalable, and applicable to a wide variety of other situations, including surveillance, financial transactions, network diagnosis, power grid monitoring, and others.