What about Pheidole pallidula?
The thing is that I live in apartement in Potugal, and even if I put them outside (I can't offcourse) I doesen't get that cold all the time.
And I realy can't put it in the frige for a cople of months neigther...
The colder it gets inside (in winter) is 17-18-19º C... what you think about this?
Normally it is a bit to high, but how does your ants react to the temperature. My Pheidole pallidula are in hibernation now, but they do not hibernate like central European ants. (central European ants almost don't come out of there nest, south European ants are just slower, they almost don't eat anything and are most of the time in there nest (underground)) So if they do that maybe they will take a short hibernation after all.
(This is an anwer in my experience ;) )