A White Orb Moving Fast

Photo date: September 27, 2014.  Photographer: Mark Mahin.

This photo of an indoor wall seems to show a moving orb. Since my camera has a shutter speed of 1/2000 of an second, a photo like this  indicates very rapid movement -- movement greater than 100 miles an hour. The photo cannot be explained as a photo of an insect. The top speed of house flies, by comparison, is only 5 miles an hour. Moreover, no flying insects were observed at this location during the previous month.

Dust level: 140/8 (Fair). Reflective surfaces nearby: none. The orb was about 9% of the full picture (vertically). No orbs shown in photos taken at same location from same angle soon before and soon after this photo was taken, which argues against any dust explanation.