Answer:
Slithery critters with a taste for dirt.
Tall when seated, short when standing.
They are producers of pies and burgers and are great for tipping.
From that which comes within itself, It builds its table on my shelf.
He's big, old and fluffy, And looking rather scruffy. He always needs a shave. It's best to just avoid him, And leave him in his cave
You use it between your head and your toes, the more it works the thinner it grows.