Once you apply bug repellent, have a ghille suit on and broth of enlightenment in your last slot. Sneak up behind it , you have to get really close to passive tame it. Aim for the back of the head, that's where the feed prompt appears. Good luck
Easiest and safest way to tame this is to lure it under water. They stop aggro and you can tame as you please. Just make sure you come up for air every once in a while. Also be sure the water is deep enough.
Tip for anyone who thinks these fart wads are easy to tame: they aren't. Before you can even think about going down a cave to tame one, you need at least one Broth of Enlightenment, which you cannot feed to them until they de aggro, which means you also need Bug Repellent. A ghillie suit is recommended but not mandatory. If you wanna try stealing one with a megalosaurus to tame elsewhere, fat chance. The game tends to despawn the arthro the moment you exit the cave. Be prepared, thats all I'm gonna say.