Insect and Spider Identification: CLOSED: tiny blue-black beetles, & pink nymphs? in night cluster , 3 by spoonlegs

spoonlegs wrote:
Okay, these cute little beetles have been "sleeping" at night in a tidy cluster on a side of a large plastic pot in our garden, western Oregon. At first, there appeared to be lots of tiny pinkish-red ones as well as larger metallic blue-black ones. Now most seem to be the larger blue-black ones, so maybe the pinkish ones were nymphs of the same species? I turned some of the blue-black ones on their backs today, and they have a red mark on the underside, like a curving upside-down Y, with the stem of the Y on their chest and the legs of the Y curving out under their abdomens. Other than that, dark underneath.
The color of the pink ones is visible in the upper left corner of the cluster in the first photo. Dandelion leaf and grass in photo for scale. When touched, the beetles break formation and scatter (2nd & 3rd photos).