Molecular diet analysis is rapidly popularizing among ecologists, especially with regard to methodologically challenging groups such as invertebrate generalist predators. Prey DNA detection success is known to be dependent on multiple factors among which the type of dietary sample has rarely been addressed. Here, we address this knowledge gap by comparing prey DNA detection success from three types of dietary samples. In a controlled feeding experiment, and using the carabid beetle Pterostichus melanarius as a model predator, we collected regurgitates, feces and whole gut contents at different time points post-feeding. All dietary samples were analyzed by multiplex PCR targeting three DNA fragments of different length (128 bp, 332 bp and 612 bp). Our results show that both the type of dietary sample and the DNA fragment size explain a significant part of the variation found in prey DNA detectability. Specifically, despite a significant decrease in prey DNA detectability with increasing time post-feeding, we observed for both regurgitates and whole bodies significantly higher detection rates for all prey DNA fragment sizes compared to feces. Based on these observations, we conclude that regurgitates and whole body DNA extracts provide similar information when prey DNA is targeted by diagnostic PCR, whereas prey DNA detections success in feces is still good enough to use this approach in ecological studies. Therefore, regurgitates and feces constitute an excellent, non-lethal source for dietary information that could be applied to field studies in situations when invertebrate predators should not be harmed.