I thought that as well when I was first suggested that but ya you would think that's too high but I found out most species are comfortable up to 35C which sounds insane I know but I have actually tested this out.
Now I use a heating cable and let me say it is very tricky and dangerous learning to use a heating cable properly, it has taken me three years of accidentally killing ants by heating them too much to figure it out. I'd say this is because many different people say many different things and you can use it many different ways. There's two ways that I prefer and definitely recommend if you're new to heating your ants as these ways are much safer compared to using a heating lamp or a different heat source.
The first way is is placing the cable under the water portion of the test tube (not directly because it will be way too hot for the ants, I recommend, for this way and the other way, placing some material in between the cable and your test tube and placing a thermometer of some kind where the test tube would go and play around with different materials till you get the temperature you desire). I wouldn't recommend using this way for ants that don't need a lot of moisture or humidity because this way normally makes the water evaporate much faster making the test tube much more humid, this is good for ants like myrmica who really like moisture but for others that don't like Camponotus, go with the other method.
The second way is heating the test tube front the front entrance. This method is my personal favourite even with moisture loving ants because this method allows the ants to regulate their brood in terms of how much heat they want to get by placing them closer or farther from the test tube.
If you'd like I can take a picture of how my camponotus are currently set up.
Edited by Karma, June 17 2018 - 6:22 PM.