This guy spawns in the center of the room on the right. I think it is about a 2 hour spawn. As far as the level required for the quest, you better be a bit higher than 18 if you are non-melee and trying to solo this. Some of the regular Heart spiders and all of the Large ones were blue to me. It's quite hard to cast in combat if you are getting bit by these damned things. Plus, if you don't root them, they will run away even if they have support there. they run straight through the pits with all the other spiders and bring them back for action. Make sure to root. I found root-nuke-nuke-repeat to work well with one spider at a time.
Now, about that poisen. Unless you have/are a person who can heal poisen, stay away until at least level 25... that stuff is quite bad. I've had my sv.poisen buff up and have several sv.poisen items and I still got hit 2-3 times in an hour from the small ones that can hardly hit me. when you have a large spider and a couple smalls on you, and you are poisened... it can be good and scary. I had to root->zone once at 20% health... It brought a train of 9 spiders to the zone. (they don't agro though)
Quess Tioneverything
Level 21 cleric of underfoot
Zeboroux