Ants need heat. Help!

[TEXASantlover]

I have a Rover ant queen and Four workers in a test tube set up. There were eight but the numbers have declined and I think it’s because they don’t have enough heat with a current set up.

What is the best heating cord?

I would like to eventually move them into an AntsCanada mini formicarium but they’re too small right now.

[Goldendoodle50]

why don't you try heating but start off far away and get closer of they like it.
BUT DON'T JUST PUT IT ON FULL HEAT RIGHT AWAY!