Actually I know this effect very well. You are correct it is a bug. The effect is caused by an insect which is much faster than the shutter speed of the digital camera. The flapping of the wings across a short time spand and the movement of the body creates this pattern You can see where the wings flop up and down. Also the areas where the white is brighter is where the motion of the body slowed down due to the action of the wings. Just as a swimmer pauses as he reaches for another scoop of water to propel himself forward, so is the motion of the insect. As the wings flip up, and prepare to catch the air and push forward the body of the insect does not move. And this creates the slightly brighter impression. Great catch! These are also known as cork-screws, fliers and have a number of claims behind them including paranormal, alien and un-classified creature. But the truth is, its a bug.
