What is Fiddleback spider in "Fiddlebacks"?

The fiddleback spider that the narrator is hunting with her siblings in "Fiddlebacks" is, much like Cimarron Jim in "The Animal Part," a symbol of childhood. Only the narrator's brother is actually looking for the spider on these outings; the narrator herself is just having fun tagging along with her siblings, and her older sister seems to simply be bored. But the narrator knows that her older sister is growing up, and probably will not want to hang out with her younger siblings for very much longer. These searches represent the end of an era.