what are these bugs?!

what are these bugs?!

I have a zinnia growing in a pot on my porch that seems to be doing well, only it has acquired a bunch of little bugs on the underside of the leaves. They don't seem to be doing any damage, yet, but I'd like to know what they are and if I need to try and get rid of them before they spread to other plants. I tried a google search and couldn't come up with anything. Thanks for any help available out there! ps: I'm in Boston if that matters.
My Recent Apartment Projects

My Recent Apartment Projects

Some of my hydrangeas

Some of my hydrangeas

Hollyhock

Hollyhock

uh oh…

uh oh…

Hats on display

Hats on display

BEFORE AND AFTER

BEFORE AND AFTER