We have a new camera system out work with complete perimeter and exit/entry coverage. 2 of the bullet cameras consistently have spider and web issues and we are always asking the maintenance man to clean them off in the mornings.... I had an issue at home with ants and other critters crawling up the shepherds hooks that i hang my hummingbird feeders on. It was constant and i tried several things until finally i found something that worked (albeit temporarily) and i think i'm gonna suggest that our maintenance guy try this with the cams at work.
Take a paper towel or old rag and spray it with black flag or raid bug spray. Wear gloves if you have sensitive skin. Then take the soaked rag and wipe all around the base/mount of the camera itself. I'm not sure how plastic/polymer will hold up to being soaked with these kinds of chemicals so be careful on getting it on or near any those surfaces. Give the area all around a good coating and see how it goes. If you are daring and the cameras aren't too far out of your reach, i'm sure you can prob spray it in a circle directly around the mount itself just be careful of discoloration of the siding/brick or whatever surface you have it mounted to. I'd also be careful of having the spray splash onto the camera itself. With the hummingbird feeders, i wiped it around the top of the shepherds hook that they were hanging on and the ants stopped for a few weeks. This effectiveness will probably vary by the amount of precipitation you get and you may have to do this every few weeks but it might be something to consider if you are having constant issues.