When the larvae are digging in the ground they will run into small stones or tree roots which they must go around. When the cicadas are underground, and sucking on tree roots, they keep going deeper and deeper. This is because the burrow was too small, or it needed a larger root. The nymph's urine helps stabilize the walls of the burrow. I have found even more information about praying mantids.
Pesticides are harmful to mantids.
To keep praying mantids alive, we must use fewer pesticides and have lots of mature plants to provide shelter for them. You also shouldn't keep egg cases. Praying mantids usually live in places with warm or tropical climates, but European mantids are native to cool climates. Praying mantids are capable to eat tree frogs. The male praying mantis has wings but the females do not.