What's that squirming between in the trees? While it might look like a solid clump, it's actually a massive group of caterpillars. A group of caterpillars is called an army and there's no doubt about why. These invaders eat nonstop, devouring all the plant life in their path and leaving nothing behind. With simple language paired with photographs of caterpillars, this volume invites young readers to learn how caterpillars start their lives and why living in an army is important.