I'm not familiar with scarab decks, but is only a gravity mark enough to power devour?
I also think you need to run more than one Turtle Shield, your odds of drawing that one early enough are slim. Perhaps you can run an anubis or two, too? 8 damage is nice, and immortalizing scarabs would be great for creature control.
Also, the obvious weakness is that you have no healing so Octane/Fire Bolt will destroy you.
Add SoG's?
You might also be pillar heavy on aether, but I'm not sure since I've only played a fractal deck with an aether mark.
Other than that, it sounds great