Dr. Tilly Collins det.

Jack -- perfect photo! Harsi -- nice call!

Moved from Tuberolachnus.

I'm pretty certain that you are safe in assuming that this is an aphid, but this family is notoriously difficult to identify and I gather that most professionals are reluctant to hazard a species-level identification without at least being able to examine the specimen in the lab. So, please do not take the following as anything more than random speculation on my part...

I thought your aphid looked sort of unique so I browsed the guide pages and found this image:



I was heartened to read that this is apparently the Giant Willow Aphid, as you had specifically mentioned that you found your aphid in a primarily willow habitat. Thus far, there don't appear to be any specimens in the guide west of Texas and I am uncertain as to the species given range or whether there are other look-alike species to consider. Still, I thought there were enough interesting similarities that it was worth conjecturing about, if nothing else.