Virtually all of the characters in There There are dealing with personal issues of one kind or another. The most significant of these issues is addiction, whether it's drug addiction or alcohol addiction. Vicky, for example, is an alcoholic, and it's no surprise when her daughter Jacquie Red Feather ends up going the same way.
It's Vicky who makes the pertinent observation that spiders represent traps, a reference to the fact that being in the grip of substance abuse is like being caught up in a spider's web. What's more, spiders also represent home, which for many of the characters in the story, is a place of chaos and instability. For them, being at home and being trapped—in poverty, addiction, and abuse—are almost synonymous.
Jacquie's spider web tattoos are another example of spider symbolism. Looking at them and thus being reminded of what her mother said about homes and traps, recovering alcoholic Jacquie refrains from falling off the wagon and taking an illicit sip of booze.
For Orvil, on the other hand, the spider symbolizes home in a good sense. When he pulls some spider legs out of an itchy leg sore that's been bothering him for a while it's a sign that he's growing up and that he's becoming more aware of his Native American heritage. In other words, Orvil is coming home to his own people.