Woolly What Now?

What: Woolly Alder Aphids!
Where: I found these on the underside of branches on a small alder tree by Spring Lake (west of the Minneapolis Sculpture Garden about a quarter mile).
When: November 21, 2012 at 8:15 am
Observers: Abbie --- I was captivated . . . and more than a little creeped out. What on earth is this bizarre stuff? Was it fungus? Something man-made? Or something unearthly and alien, which seemed just as likely. So I contacted a professional naturalist friend of mine who identified these Woolly Alder Aphids.
Conditions: Breezy and brisk