What I did was melee the thing with two normal anti-poisons, two prayer potions, and sharks for food. I melee'd it with rune armor and a dragon scimitar. During the fight: It uses melee and range, I believe, so don't worry about prayer then. Once it starts getting help, then I protected from their attacks, and took them out, but just attacking the beetle and ignoring the other monsters that appear to help it, might work.