The praying mantis is well-known for two things: 1) the posture that makes it look like the insect is praying, and 2) the fact that the female often devours the male throughout the mating process.
One of the most frequently-asked questions about praying mantises is why the females consume the males after mating, and it turns out that there's a valid reason for it.
The copulation process between two praying mantises can last for extended periods of time, so the male needs to keep the female entertained throughout the process. One of the ways he can do that is to let the female eat his head, after which the now headless body continues pumping sperm into the female's reproductive tract.
The male's body will keep going until the female devours every bit of it. By this time, however, a substantial amount of sperm has already been deposited into the female's reproductive system.
While the male might not be around to see it anymore, the vast amount of sperm he deposited into the female while he was getting eaten has a high chance of yielding offspring. That said, his act of transforming into an entrée increased his odds of successful reproduction and completed the circle of life.
As it would seem, this bizarre mating tactic works great for several praying mantis species.