Arachnophobia (3.5e Trait)
From D&D Wiki
You have quite the fear of spiders and other arachnids.
Benefit: You gain a +2 dodge bonus to armor class when attacked by arachnoid creatures (i.e., any creature resembling a spider). You are quite good at getting out of a spider's way...
Drawback: If, at any time, there is an arachnoid creature within 10 feet of the character that she can see, the character must pass a Will save (DC 15) or become shaken. This distance increases to 15 feet for Tiny arachnoid creatures, and by an additional 5 feet for every size category increase in the arachnoid creature. The Will save DC increases by 2 for a Tiny arachnoid creature, and by 2 for every size category increase of the arachnoid creature.
Roleplaying Ideas: You probably suffered for it when you were younger at the hands of your friendly neighborhood spider-freak. "Oh, no. I am NOT going into the underdark to confront the drow. They worship Lolth! The SPIDER goddess!"