If there are too many praying mantids, they'll take care of it themselves. More likely, if you want more mantids, you will have to take matters into your own hands. If you have a climate that supports mantids, and you find several egg cases in one location, you might consider moving the extras to bushes that lack them. More likely, in our area, you will have to buy egg cases and place them throughout the garden. With our coolish springs, you might have to hatch them indoors.
Most commercial sources have instructions on how to store and release the egg cases.
This irritates a mantis greatly, causing it to pinwheel its strong forelegs trying to get hold of you. Rating Good Guy , sort of. Although some may argue with this, praying mantids are not particularly effective as beneficial insects. A few mantids, however, are not going to do great harm either, and can be considered as one part of the arsenal of good bugs in your garden. And a fascinating one.