This sucker is not passive. Me and my friend were running through the forest and this thing jumped out and killed me. When I came back to get my stuff, it lunged 20 feet and killed me again. After the third death I gave up on recovering my stuff. It was not tamed by an enemy tribe because it was me and a friend on a private server.
The mantis has two attacks, the close range hack and slash, as well as a devastating pounce. The pounce attack is long range and does considerably more damage than the hack and slash. Mantis aggro from a considerable distance (as in, if your on foot get out of there fast) so the pounce attack is very deadly. However, fire damage weapons i.e. Wyvern fire, flamethrower etc. do more damage than other rounds, the same goes for other insect/arachnid creatures