SHOO FLY

I'm not found on the tip of the tongue,

But I'm usually quite close by;

Add a letter and you will see

That I'll soon take wing and fly.

HINT #1: It's not the human tongue.

HINT #2: The title is a clue.

Answer (in verse):

Hang your head if you missed the clue,

For the title word indeed is shoe.

A shoe has a tongue that is covered in lace,

With an AGLET at its tip

To keep frayed ends in place.

Add an E and you will see

As clearly as the eagle does,

That the EAGLET will soon soar high above,

As soon as it loses its downy fuzz.