Although we have seen mantis´ egg sacs (ootheca), this is the first time that we see one actually laying. It was discovered in our garden by Mabel who is also responsible for the images.
A quick search suggests it to be Miomantis caffra, the springbok mantis and the egg sac would contain up to three hundred eggs.
This species, like other mantis, exhibit post-copulatory cannibalism. But it also can devour the male before mating and she is able to lay fertile eggs even when not mated! (1)
(1) I will not publish my wife´s comment in this regard!
The two videos below show the mantis in action.