I'm having a bit of an ant problem in some of my tubs. I am using Sterlite tubs with paper towel as substrate and I use flexwatt under the tub at the back for heat. Every other day or so I notice ants inside the snake's tub. Very tiny ants. They gather under the paper towel and I usually find a bunch in the water dish. I have examined the snake thoroughly as have other members of my family and we never see any ants on the snake itself, just underneath the paper towel and in the dish. I used to have aspen as a substrate and took it out in favour of the paper towel so I could get a better handle on what was happening in the tub. I have ant traps outside the bottom tub on my rack (the tub most affected) but it doesn't seem to help much. I read that lemons can help (?) Is there a safe alternative to put in the tub itself or can anyone recommend a better solution to use outside the tubs?

Thanks for your help!