On ragarock they spawn like everywhere in the black zone! So when you land your argy for water make sure to spicy out the area first. Last three argys to mantis, came back a few days later with a flame thrower now we eat cooked but meat, tasty.
I can tell you from experience that in fleeing this bug you only need 1 tranq. Yep i shot that thing into my tribemates knee and was able to escape at a brisk pace as the mantis ate him