Insectivorous bats feed on a wide range of arthropods and play an important role in agriculture by reducing pest populations. Brazilian free-tailed bats (Tadarida brasiliensis) are known to typically consume moths and beetles, but little is known about how their diet changes across seasons or towards the edge of their range. To investigate these questions, we analyzed guano from 20 bat houses in Butte County, California, collected from December 2023 to November 2024. DNA sequencing identified prey and confirmed that nearly all samples belonged to T. brasiliensis. Unlike previous studies, in Northern California their diet consisted of less than 5% moths (Lepidoptera). Flies (Diptera) dominated, representing over two-thirds of all prey, followed by beetles (Coleoptera) at roughly fifteen percent. Diet varied significantly between seasons. Winter was dominated by Diptera (93%). Spring also showed a dominance of Diptera but a notable rise in Hemiptera (24%), likely due to increasing aphid abundance. Summer had almost equal proportions of Diptera and Coleoptera (43% and 44%) with the highest Lepidoptera of the year (10%). Fall was primarily Diptera (79%). These results indicate that T. brasiliensis likely switches prey with seasons, relying on available insect groups when preferred prey are scarce.