If you are to tame a mantis I would recommend you try to tame it where it is far away from anything that it can Agro on or else you will have to start over. Don't tame these guys in big numbers I'd reccomend, at most, two at a time so you don't get distracted or lose sight. I also reccomend that you don't try taming one of these guys until you are absolutely ready with repellent and horns. Beware the horns are heavy. Good luck!
Please don’t listen to the boy who said with bug repellant, ghille and cactus broth that the aggro range is “literally zero” cause it’s not.. you can get super duper close without aggravating it but you can’t get too close so still be careful and try not to stand so close you can touch it or it will STILL AGGRO.
On Fjordur, you can find rocks in the volcano area that resemble fossilized Death Worms, which can be harvested for Death Worm Horns, making taming them much easier there, if you have the rest of the necessary equipment
While it is cheesy and very hard to pull off on most maps, if you can lure a mantis into swimming deep water, then they either chase after you and then lose agro and dive underwater or they lose interest immediately and return to shore. After they run back to land/dive, you can get a free feed while they swim back with next to no chance at an agro, plus their food drains a little quicker because of the swimming.
P.S this was already said by other people but my comment spreads the taming method easier (I'm blatantly stealing)