Need help with bug

Last night I discovered a bug (actually many of the same kind) on one of my young sour cherry trees. I really couldn't see it well enough, the whole tree is so gross. I really didn't want to get close, in the dark. (Ok so I'm squemish.) The tree is horribly infested with aphids as well. Lady bugs are to the rescue there.

I do not want to do anything unorganic. I posted a picture on "garden foes" page. But, it wasn't great. I can't seem to get close enough without blur. In the light of day, I have put several in a jar and looked closer. Here is the description. These creeps have six legs and chompers. They are black with spines, segmented, have pale underbellies, and use their tail end to manuever and grab on with. It seems to function like a suction. They are definately chomping leaves. I now have enough info, I hope, for a search. If you have any information you think might save this poor tree, please let me know asap.