If you wanted to culture them, you would need a queen. She's the gal that lays eggs all day and is fertile.
"Harmless to people", sadly, isn't a helpful rule of thumb for feeding your mantids. It all depends on what instar your mantids are. The thing about ants is that, while some may not be able to get a grip with their mandibles on human skin (sugar ants can, though. I've had many instances were they bite me and hang on for a while, just by their jaws.), all it takes is a not-so-precise snip to remove the leg from a small mantis. And in groups, ants can take down much larger prey.
So, if you want to set up an experiment, give one to a mantis of yours. Give the mantis at least 24 hours, maybe longer, to show symptoms or signs of not doing well. And be sure to share your results with us!