Arelith

Not sure what the intention was with giving the Bugbear Shaman cleric Summon Creature IV (Dire Spider). But it is rather unrewarding, and frustrating, for the challenges it presents from my experiences with it so far.

You can prepare for these by using scrolls, or bashing them into oblivion before they can use the spell. I know that's not any consolation, but it should inform how you approach that encounter. It does make summoner mobs difficult in early level, but that's where your character learns the imperative of approaching these enemies with caution and tactics.

It might surprise you that the spiders only require level 7, which should be about where the bugbear shamans are in level. I'm always glad they don't summon something stronger!

You could try hitting the shamans with ranged weapons if you're skilled with them to disrupt them; or even bringing your own summon to the fight.