Abstract: A system for monitoring rodents in a sewage system, the system including a plurality of monitoring devices placed in manholes of the sewage system, wherein each monitoring device is provided with one or several sensors configured to detect rodents in the sewage system and to generate a sensor data set. A memory configured to hold an identification code, and a data communications module. A server includes a data communications module communicatively connected to the data communication modules of the monitoring devices, wherein the server is configured to receive, from each monitoring device, the sensor data set and the identification code, and based on these data sets identify how populations of rodents move in the sewage system.