Praying mantises spend a lot of time, like spiders, staying absolutely still and waiting for their prey to come near. But as predators, mantises, such as our nearly mature Tenodera sinensis nymphs, also need to keep the tools of their trade clean. The most important, and deadly, tools are their spiny and serrated raptorial front legs. To keep them clean, particularly after a meal, but also regularly at other times, the insects chew on them. They also clean their long, filament antennae, pulling them down into their jaws with a leg and then chewing the entire whiplike length clean.
These two T. sinensis are siblings, yet one is brown and the other green. Most mantids of this type, like Mantis religiosa, our other species here at home, come in both green and brown morphs, depending on factors like humidity and vegetation where they grow up.
Our biggest T. sinensis has wing buds on its back, which means its next molt will likely be its final one, to the adult imago stage.