I had the same issue recently 1st time I ever seen it. I did notice the rubber seal on the bottom of my camera wasn't tight so maybe that's how they got in. Sorry I couldn't provide advice but letting you know your not alone.
I just had one last week. clean it out and place back. What was worse was 20 to 30 deer ticks crawling over the one cam, i looked at it for 5 minutes making sure i wasnt seeing something other then deer ticks, It must be the heat or something inside the cam. I spayed the outside with permethrn and havent had the problem.
I lost one last year to ants and had another filled with them a week or so ago on the same tree. The camera was still working this time so I scraped them out and moved trees. However, I was kicking myself on the way home as I remembered last year they got into components of the camera you couldn't see, so I should have taken home and tried the freezer trick. I hope they take it easy on chewing the wires till I can make it back, but it will be another couple weeks.