Brown Creepers are common but easily overlooked Minnesota birds. I have banded 18 of them since the end of March. Because they are drab and poke around tree trunks, Erika refers to them as tree lice. Sibley calls them "tree huggers." They are woodpecker wannabes; they have stiff woodpecker-like tails, but their toes are like songbirds--three toes forward, one back. DNA studies suggest creepers are most closely related to nuthatches and gnatcatchers.
On the other hand, woodpeckers, like the Pileated, have two toes forward and two toes back (see the lower toes on the next photograph.) If you want to impress your significant other, you can tell him/her that songbird toes are anisodactyl, whereas woodpeckers are zygodactyl.
Exceptions among the woodpeckers are the Three-toed and Black-backed woodpeckers. They have three toes (two forward, one back). Curiously, despite this morphological difference, these two woodpeckers have recently been lumped into the same genus as Hairy and Downy Woodpeckers, which have typical woodpecker toes. Note the toes of this Black-backed Woodpecker.
I think it is a bit unkind for Erika to say that Brown Creepers are Tree Lice. Brown Creepers actually have lovely, chestnut and white-speckled rumps (seldom seem except when the creeper is in hand.)