This bug is angry and defensive, when threatened it raises it’s large tail like a scorpion and opens it’s pincher mouth as wide as it can. It looks like an ant but it’s tail section looks to have several parts and is about 3x it’s first two sections. What is it?
You have found a Rove beetle. Unlike most beetles the hard wings on the back only cover part of the abdomen(the tail section). Since you are in the Bay Area of California, you may have the Devil’s Coach Horse rove beetle. These are 1 – 1.25 inches long…how long was the one you saw? This particular rove beetle is known for it’s defensive posture…so besides the pinchers and tail raising they can also spray from stink glands.
Rove beetles are predators. If this is the Devil’s Coach Horse rove then it eats snails, slugs and other pests. So, it might be a good critter to keep around in the garden.
Moni has an ebook “Garden Insect Pests of North America – Pictures for Identifying and Organic Controls” Check it out!