Yes, they do love caterpillars! In the woods here they are so easy to find in this time of the year. I also fed them a cricket (I use these to feed my M. rubra, they don't seem to like caterpillars much) and they loved it as well. They also like my honey-water solution. Does anybody have any experience with honey-milk solution? I have read this on a French forum and the idea seems good (proteins and sugar, what more could you want!) but is milk healthy for ants?
I still keep them in a test tube at the moment, the colony isn't very big. It has 2 queens (

) and about 35 workers. I hope it will grow fast (because it has 2 queens this should be on problem!). Their speed is quite nice though, just strange that they aren't very aggressive (I guess this is why F. sanguinea likes to rob their pupae).
Yeah, heating them could be very risky, especially if they do not have enough water... and if they have too much water it could evaporate a bit and this species doesn't like moist environments. Though my room is usually quite chilly (my windows point northward, and I have shadow from trees all over my room) so I guess heating them a bit might not hurt. But I will not take the risk yet

. Wouldn't like to lose the colony! Better to let them grow slower than to get them killed.