What kind of bug is this?

There are wasps that somewhat fit your description, namely ensign wasps - a href="http://bugguide.net/node/view/14164/bgpage." rel="nofollow"http://bugguide.net/node/view/14164/bgpa…/a Very small, usually only a few millimeters in length, with large eyes and long hind legs. Without a photo it's impossible to be sure.