The Spider House: Battle for the Wall — Steven Jenkins

Behind every wall in every house, there are spiders-spiders with families, communities, and lives of their own. They hunt, spin webs, argue with their parents, avoid bathtubs, and occasionally take pleasure in spooking the humans (and live to tell the tale). For the most part, days are routine; however, for young Bateman, everything changes when he slays the sinister General Raimi, leader of the powerful and vicious Spider Army.
Fearing for his life, Bateman flees the confines of The Wall. He's always dreamed of exploring the house and garden, but not as a lone fugitive. Danger looms everywhere, as does the little girl of the house. Unlike the rest of the family she's not in the least bit scared of spiders, and has enjoyed tormenting and torturing the little critters for years. That's why they call her "The She-Devil"-she's every bug's worst nightmare.
If Bateman is ever to return to the comfort of his family and friends, he must face the Spider Army's fury and the vengeful General Raimi II. With the thrilling and wickedly funny adventures of Bateman and his unlikely allies, you'll discover what it means to be home and what it takes to be a hero. And you'll never look at your average arachnid in the same way again.