These things are at the base of a crape myrtle and it appears they have come from the ground beneath them They are too big to be aphids and when I approach them they spread out in what looks like a football stadium wave.
Bark lice, aka 'tree cattle' - harmless. http://escambia.ifas.ufl.edu/blog/2012/04/27/bark-lice/
alice, i had those on a tree in the keys and remember having a devil of a time finding an ID. tg for dg.
ps. those aren't like the ones i told you about on my crinum this morning....should have taken a photo before i soaped them.