Best for Last?

I was planning on saving these ghoulish critters for a halloween post, but I couldn't hold out any longer! Hold on to your breakfast and read on!

Fred Heath wrote to Eric Eaton (main author of the Kaufman Field Guide to Insects of North America):

[A]t a meeting of the Native Plant Society, one of the folks came up to me and described some bugs (non-scientific definition) that got all over his clothing after bushwhacking in Ironwood NM. He said they almost looked like tiny scorpions with their tails held up in the air. I asked if he had a photo and the answer was no. Since I had no idea what he was talking about, I figured to just let it go.
On Thursday morning [9/10/2015], I was walking around Sabino checking out Canyon Ragweed (Ambrosia ambrosioides) which I just recently found out was a host plant for Bordered Patch, when I found a well-eaten plant and checked it for the patches. To my surprise, what did I find, but little scorpion-like insects (at least they seem to have 6 legs), the like of which I’ve never seen. I’m thinking they might be some sort of beetle larvae, but I really don’t have the foggiest idea.
I did, however, take a few photos. They are clearly eating the ragweed. Can you help clear up this mystery and tell me what the heck they are?

Photos by Fred Heath 9/10/2015

Eric responded: 

The insects in the images are larvae of the Arizona Tortoise Beetle (Physonota arizonae), or a very close relative. They wave their poop around on the end of the abdomen, presumably to deter predators. 

Fred says:

Mystery solved!! See Margarethe Brummermann’s excellent larva photo, too!

Anne says: This story continues...