The Gorgle by Emma Fischel

Finn doesn't want to move to the spooky old house in the first place. Soon the strange goings-on and mysterious noises are driving him crazy - and he's driving his family crazy about it. Then he sees the creature that's been hibernating in the wardrobe...
It's a Gorgle. A bit like a moth, a bit like a hornet, and a lot like a ten-foot-tall monster from your worst nightmare. It's awake. It's hungry. And Finn is the only one who can stop it!