Do they all
hatch on one day and then....poof? Educate me.

When I was looking into these last year, I read that they pretty much
kill each other or are killed by predators until there are only 1-2
survivors. They are very territorial.

I was pruning the shrubs and a mantis as big as my hand crawled out.
I relocated it to our patio area landscaping, but we have a cat, so I
don't know how it fared.