Billywigs are little insects with stingers underneath their bodies.
Just one sting of a Billywig will cause you to get a case of the giggles and start levitating.
Naturally, little kids like to mess with them. Of course, you don't want to get stung too much or you end up floating for days.
Bowtruckles are peaceful little creatures (only about eight inches tall) who live in trees.
But if anyone tries to mess with their tree—watch out—they've been known to jump down and attack.
It's best to offer some treats (like woodlice) if you're just looking to take a bit of wood or bark and then be on your way.
These guys are straight up pests. They're pretty good at getting under your house and rotting away the foundation. (The joys of being a magical homeowner.)
You'll smell them before you see them, which is good. You can get rid of them with Scouring Charms, but may have to call the Department for the Regulation and Control of Magical Creatures (Pest Sub-Division) if it looks like your house is about to totally collapse.