Urban wetlands are important habitat for wildlife, particularly insectivorous bats which provide a key ecosystem service in suppressing insects. While claims are often made that bats consume high numbers of mosquitoes in a given night, the evidence for this claim is scant at best. The Canning River Regional Park (CRRP), an urban riverine reserve in Western Australia, has fauna conservation as a primary goal and mosquito control as a top priority. We took advantage of occupied bat boxes within the CRRP to determine the roosting bat species and their diet using non-invasive DNA metabarcoding of bat faecal samples. The widespread and urban-adapted Chalinolobus gouldii was the only bat species detected roosting in the bat boxes. This opportunistic forager consumed over 700 unique prey (operational taxonomic units; OTUs); only 14% of OTUs were assigned to either species or genus, representing seven insect orders. Mosquitoes were detected in 11% of the 90 faecal samples, over multiple years and in both the maternity and non-maternity seasons. Assigned prey was predominantly Lepidoptera with 40% of the 49 Lepidoptera species negatively impacting humans. Urban riverine reserves are critical habitat for bats, which in turn, are crucial in providing the ecosystem service of insect suppression.