An Army of Frogs by Trevor Pryce

Darel is a wood frog living in Amphibiland, and he dreams of becoming a Kulipari warrior, like his father. His father was a hero and died years earlier while defending the frogs against the scorpion army. Amphibiland is now shielded against its enemies by an invisible cloaking spell. However, the scorpion king and spider queen are joining forces to invade the land. The queen thinks she can use nightcasting to undo the spell, so the scorpion army can attack and kill all the frogs. Darel accidentally finds the enemy forces and must secretly join them to free his captured friend. How can one little frog beat an entire army of scorpions, spiders, and mercenary lizards?

Darel is a character with dreams of glory, but he also has the natural fear that goes with war. He is mischievous and frequently gets into trouble, but he is a very loyal, brave friend. The author did a good job of creating suspense and finding ways to add twists to the conflict. The reading level is probably appropriate for middle grade readers.