My son and I saw it on my Maple tree today, 6/16/08, 3:30 pm,just before a rain/hail storm. It was "flexing" it's abdomen, or butt? The two fine black feelers, or legs? were poking the large black abdomen part like it was going to lay eggs? At first we thought it was two insects mating, but after closer inspection it was touching itself. It didn't move anything other than it's head when I got close with my finger tip. We didn't want it to fly into our faces so my finger is as close as I could get, without disturbing it. It didn't walk either. After the storm 15 mins later, it was gone. We looked everywhere, as we felt it had blown off the tree trunk, but it must have flown away. Very, very scarry. I've looked through your wasp photos and some are close, but this has a smaller yellow head/face, your thread wasps all have large black faces. Good luck, we are both very curious, so please let us know.