The mantis (Na'vi name: fwäkì) is a flying insect that has co-evolved with the mantis orchid. It can change color, camouflaging itself from predators, or to ambush smaller insects, reptiles or small mammals. It is not poisonous, but its size means that it can still inflict serious harm to Na'vi and humans. Its co-evolution has meant that it appears very similar to the mantis orchid, and its mouth is a perfect fit for the flower of the orchid.
Source
James Cameron's Avatar: The Game - Ingame Pandorapedia entry for mantis orchid