There are a lot of videos on YouTube showing praying mantises stalking hummingbirds at their feeders. Douglas Main at Popular Science says that this is because the hummingbirds are being eaten by praying mantises but the researchers watching usually attempt to rescue the bird.
But, after a bit of research, it seems pretty clear that mantises are capable of catching hummingbirds. In this 1982 study in Biological Reviews, the authors report that praying mantises can indeed catch small hummingbirds. "Praying mantises reach a length of 98 mm [3.9 inches] and may feed on small birds," the authors write. However, "the actual observations in the literature are inconclusive as the captured birds were ultimately released by concerned ornithologists," they continued, somewhat perplexingly, since it is generally frowned upon for scientists to intervene in the lives of the animals they study.