Snowy Swirl in Front of Cam like Bugs

There is a swirl or sometimes driving lines in front of my camera at night sometimes. It looks like a snowstorm or driving hail storm. It sometimes looks like bugs flying. It happens outside and inside. After looking at it and cleaning it, it still occurs. It was not snowing, hailing, or downpouring rain. There were no bugs flying or crawling. The cam inside the house had frequent streaks but not nearly as many as outside. Someone was home and cleaned the lense and saw no bugs while I continued to see the moving lines with him there. This movement does not set off the camera. All cams are external stickup cams. As you can see from the pictures, this problem makes it difficult to see what sets off the camera. Why does this sometimes happen? Thank you for any help with this problem.