Because some were half the size of the largest, I took a control shot of my thumbnail against a single flower head of the Verbena as most were found feeding on its pollen, with fewer going for the florettes of the Budliea whose size was easier to judge.
The most striking variety was a bright yellow that I had not come across before, and one looked very like a bee. I was lucky to get a few shots where the insect was still in flight, but a couple had just taken off and remained in frame from when I was taking a shot whilst they were static.
I started off with the flash set to one third over exposure and the ambient set to one third under, but eventually I set the flash to a full stop over and the ambient one and a third under with a few changes of ISO from 1600 down to 250 when the sun was fully out and I was shooting around the edges of the verbena clump.
I was reasonably happy with the end result considering how few were around despite the warmth.