Devil's Coach Horse, we believe

My alien superbug?
July 21, 2009
I am wondering if you can help me identify an insect?
A few years ago while I was living in Pacifica, CA (near San Francisco), I noticed this strange and aggressive insect. I cannot figure out what it is and have described it to many people, none of whom know what it is either. I have attached a drawing of what I remember it looked like.
I saw it on two occasions, both times on the sidewalk on sunny days, a few months apart. One was about 2 inches in length, the other about an inch and a half. They had black, unsegmented, hard looking body with a satiny sheen. It had no wings, but the back of the abdomen which came to a pointed tip could be curled and raised threateningly like a scorpion’s tail.
Both behaved in the same way. Upon seeing them I stood over them to get a closer look. The insect quickly noticed me and stopped walking. It turned towards me, curled it’s tail over its back so point faced me. As I walked around it, the insect whirled on its feet keeping its face and stinging tail aimed at me. It could move quite quickly. It stayed there for a few minutes until I left.
Thanks for your help! I hope you can help me figure out what it is.
Pacifica, CA

Drawing of a Devil's Coach Horse
Drawing of a Devil’s Coach Horse

Hi Roni,
We are guessing you saw a Devil’s Coach Horse, a type of Rove Beetle based on both your drawing and your excellent account of the observations.  They eat snails, so we love them in our garden.  We haven’t any files on our current computer, but we will attempt to search our archives so we can post a photo from a March 16, 2006 letter with your letter.

Devil's Coach Horse
Devil’s Coach Horse

That looks close enough to my bug- so I think you got it.  Thanks very much!  

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