You can damage them? O.o
When I did it, I just made my way around the left side of the Island, throwing a flare when a Doppel appared (Donno if it did anything, but meh) and took out the psi Bugs, ran pretty close to death a few times so having a decent stock of Health Hypo's and Bandages is a must.
But they didnt do to much damage, they were there for about 2 turns in combat, didnt really do much damage per attack either.
Didnt even know their was a Monolith, just tried to do that part as quickly as possible, as I got a strange feeling when on that island