Designed this simple test tube portal for 16mm test tubes.

The tunnel can be covered with transparent material. I cut a trip out of a transparent PET juice bottle. Because the plastic is curved slightly, it presses down nicely and ensures no ants can escape. I pierced some holes in the plastic to allow the ants to breathe.

I have no experience with ant keeping (other than killing my first queen), all feedback and suggestions welcome.

I printed it in ASA with 10% infill, it came out ok, but one of the corners lifted a bit. PLA might be a better choice.