As they take place in the same area and at the same level, it is recommended that you also get the quest Finding Millie and do them together.
If you speak to Zintra again after the quest is complete, she will ask if you want her to show you the results of the quest. If you say yes, she will apply the illusion to you, and you get an awesome drachnid illusion for a while.
From the main road between J'Rais Bridge and N'Mar's Ascent, take the path east that leads to the owlbears. The spiders will be all along the road next to rocks, nearish ( -615, 30, 40 ) /waypoint -615, 30, 40.