Well, there is already a Shadowling Guardian, so that's a bit of a repetition. I prefer void bug over abyss bug myself.
I also imagine this kind of bug to be quite old, with a touch of grey, for which I think of Gloom Bug or Dusk Bug, though that doesn't sound quite as good. How about Night Bug or Twilight Bug?
Also, given that the Shadow Bug enemy set is a medium difficulty one, I think this bug be better equipped with a non-area attack, but quite a powerful one none-the-less. How about Double Strike worth 18 damage? And then Melee as a counterattack for 11 damage? I think that would be quite nice, as the enemy would then formally have 2 attacks.
Come to think of it, with regards to the original proposed name, why not drop Shadow and keep it simply Guardian Bug? Given that the bugs also have a queen, that might be a nice parallel to have!
And I am definitely for expanding the Shadow Bug set: this could allow for more variety in map making with regards to the Shadow Bugs (and maybe party use that in the Gelf side quest

).