To tame an Arthropluera(Mobile):
1. Tame a Pulmonoscorpius...you can unlock their saddles at a pretty low level.
2. Have at least 15 Spoiled Meat in your inventory.
3. Enter the cave of The Hunter (In the south of the Island).
4. Find Arthropluera.
5. Have spoiled meat in your hot bar, target the arthro, and scroll to spoiled meat..it will automatically feed it one
Note: only click on or scroll to spoiled Meat in your hot bar if the nametag of the arthro has a blue border.
6. Once tamed, exit the cave(don't worry about leading it out...it won't work).
7. Open inventory.
8. Click on profile.
9. Click on "Tames" button.
10. Select arthro, and hit 'Request'.
11. The Arthropluera will be teleported to your position.
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.
1. Make some bug repellent
2. Get some Broth of Enlightenment
3. Go to Cave of Hunter and kill basically anything in the caves but leave the Arthro you wish to tame
4. Get some distance between you and the Arthro and take the bug repellent
5. Dismount your tame and walk up to it and give it the Broth of Enlightenment (took me only 1 with a 10x Soothing Balm to get a lvl 130)
6. Bam!!! You can run the Cave of the Strong and Immune without even being attacked
Hint: I did this on mobile so not sure if this method works for console and PC