Michael Dahl 
Terror Woods [PDF ebook] 

Erro and Zak Nine are hiding in the Phantom Forest, a dark wood filled with giant, towering trees and dangerous beasts. The boys hide high above the ground, climbing and jumping between the tree branches. So far they’ve avoided dangerous creatures such as huge, hairy rats and giant, bloodthirsty spiders. But a new predator has caught the boys’ scent. An enormous flying serpent chases after them and won’t stop until its hunger is satisfied! How will Zak and Erro avoid becoming dinner for this deadly new monster?