You better believe a praying mantis will eat a hummingbird.
This isn't the first time we've seen one of these predatory insects kill and eat a bird, but it's hard to believe it when you see it.
While they may not sit and eat every scrap of the bird, a mantis will stalk and kill a hummingbird right off of your feeder.
Here's another example of a mantis preying on a hummingbird:
Short of shooting one with a shotgun, there isn't much that you can do to stop it from happening. Since most mantids can fly (usually only the males), you can't exactly try to block the feeder.
It can happen anywhere, but it's probably more likely to happen to a feeder regularly visited by hummingbirds.
Have you ever seen this happen before?