The picture of sloe bugs is interesting. I photographed the insects in the attached picture two years ago, in mid-April. There were far more of them than are shown in the image and they were crawling all over the vegetation in one small area. The insects were photographed in Pembrokeshire on an overgrown rockery.
At the time, I tried to identify them but I wasn’t successful. I believe they are of the same species as the ones that John photographed. I think the insects are being attracted to each other rather than to a particular plant. I guess that one or more of them are sending out chemical signals to attract mates.