Friend or Foe?

ExtraDays started it with the Fuzzy Wuzzy, so I had to join in. This black bristly thing is common in our garden, but I don't know what it turns into. When first seen, it looks and feels like a little brush. As it moves the segments become apparent, and the red dots. It was hard getting a photo--while it was on my hand it did not stop moving-- crawling up, down, over, stretching, wagging. It did not like me and was trying to get off.When I put it back on some leaves it was immediately quiet.