This afternoon I wandered up to the shooters' decoy ponds near our house to check out the bog vegetation while the water levels were fairly low. I didn't find anything startling botanically - in fact nothing I've not seen here before - but the margins of the ponds were almost buzzing with small damselflies. The ones that settled so I could get a clear view were like the one in the photo (not mine, I'm afraid). A bit of internet searching suggests that I was looking at immature Black Darters (Sympetrum danae or, previously, Sympetrum scotica). If I've understood the info correctly the adults lose the golden colouring on the abdomen.
I've no idea how common these are in our area, but I don't recall having noticed them before.