Antje did not use a strobe light. But she shot this exposure probably against the low setting sun, and I would say at about 1/20 of a second. These flies have a wing beat of about 150 / second, which means they beat their wings about 8 times in a 20ieth of a second. (you can easily count 7-8 wing beats for each fly). The reason for this strobe-like exposure is that the wings reflect the light very briefly each time they are in a certain position. It´s very rare that you have the right conditions to take such pictures - perhaps just a few minutes before the sun goes down.
