As ever ones said the only way past these things is to hit them with range spells, flame strike or flame drop being the best. They are quite thick and you can het them to try and follow you thro small gaps, thru which they can't fit and then sit at a distance and blatt them. There are a few places in the trees that you can get them stuck.
Don't however, when you get to the Boogerie pit think it would be a good idea to lock you self in the room with Grunaxe's ghost so you can blatt them tru the gate as you can't get back out.
There are some instruments that fire fire so you could try sonic attack
