A bee, captured as it flies towards the lens.
Practicing with my Canon 100-400 and a Flash Extender attached to my 580 EXii Speedlight.
The idea is to take the shutter speed up until the ambient light is no longer significant. This makes the background drop into the shadows or, as here, go black.
You need to set the flash to High Speed Sync mode because at 1/1000 of a second, it isn’t going to be able to evenly illuminate your subject.