New Wilderness — Brian S. Matthews

By day it's cats and dogs, by night it's mice and rats, and if the birds don't get you then the insects will. But hey, that's life at the bottom of the food chain. One normal summer day, every mammal, reptile and avian on the entire planet unite with a single goal: the extermination of mankind. Three days later the insects join in, and it doesn't stop. It never stops. Ten years later, scattered pockets of humanity fight to keep flesh and sanity intact as they strive to unravel the mystery of what made the animals change, and more importantly, how to change them back.