A few days ago, I went out to the American River in nearby Fair Oaks with the Big Guy; I wandered around with my camera while he was busy fishing. It wasn’t until I decided to join him on the river bank that I noticed the nearby bushes were absolutely covered in small dark blue beetles. They were so tightly packed together in spots that on first glance, I actually thought I was looking at blackberries!
It turns out these are cobalt milkweed beetles, and on closer inspection many of them appear to be gorging themselves on milkweed plants. I’m still not sure if every bush I saw them on was a milkweed plant — although, according to Wikipedia, there are over 140 known species of milkweed. I do know that when I returned to the same spot three days later the beetles were still swarming but had moved up the bank to a different group of bushes.