Tips for fruit flies/gnats?

I keep my snail terrarium on my garden table (I figure if they come from my garden, they can handle the weather out there) and I have a problem with all the gnats. I know I need to remove their food during the day, and I have a pillbug or two as a cleanup crew, but I’m not really sure what else to do :( if anyone has any tips I’d really appreciate it, I can only light so much incense haha