These critters seem to have a noticibly higher magic resistance than the other MoBs in the Halls of Testing.
As a Shaman, I use disease based spells on these, including the disease-resisted slow (Plague of Insects, 25%). It's not nearly as good as the magic-resisted slow (Tugur's Insects, 75%), but at least it will land. I don't even bother trying to cast magic-resist spells on these anymore.