The mating Stylops I observed 27 March in my living place, Amstelveen (bordering to Amsterdam); one week earlier I observed a solo male on Willow catkins, but the photo of that observation is not sharp as these male Stylops love to fly - no rest for them.
The stylopised Andrena was one week later, 3 April, also in Amstelveen.
At the Dutch forum we now see a lot of Stylops, mostly stylopised female Andrena's. I was primed for my observation since it is described that the parasites influence the behaviour of the female bee. And I thin this is true; my Andrena was mesmerized, or almost paralized. I could easily pick it up and put it on my hand. I have seen the full behavior, the Stylops landing and approaching the bee, creeping below it and then finding the female Stylops. The bee just let it happen.... So if you see a tranquile Andrena, it is worth a try!