do these traps work?

I was always intriqued by these plants that eat stuff like flies. Here's the impulse buy for Joel's birthday. His photo on left. Notice the far left trap. Five days later, my pic of the leaf/trap blackened. Has it caught something? Does it kills the food and then digests it and itself as well? One noble sacrifice? What happens if they all catch a fly at the same time? Or is the black trap suffering a venus virus?