I use evergreen (washed) pieces and by pieces I mean, none of them are larger than 1/2" flaked in bottom of housing, if any extra water gets loose the mantis babies are able to walk on the leaves and escape the water. I have seen many fall into the water drops and cannot get out, thats why I use the evergreen pieces, they are easy to clean, and stay fresher than most anything.
Cool! I'm glad it's as simple as a misting bottle! I was starting to fear I would have to search and find some fancy 'moisture gel,' like I ended up doing for my crickets once.
I also like the evergreen pieces idea, I might have to try that some day.
On larger mantids drowning is not an issue, but with new L1/L2 you can definately stick them to the side of the container and drown them. The largest nursery @ mantisplace.com has a lower hole with a foam stopper in it so you can spray the bottom part of the nursery without hitting most of the nymphs who like to be up high. It seems to work well for this problem. We developed this because we killed a bunch of nymphs by sraying just a little too much...I bet most keepers have had the same experience.
You can see the Nursery at www.mantisplace.com under "Mantis Nurseries." If you get the 80 ounce insect cup it is hard enough plastic to drill a hole in it to try it in a smaller version