If the black food in mantis belly smells undigested, it might be protein over load and or if the room temp falls below 75F. Try feeding less and sometimes coat food with honey ans pollen powder.
I put the 32oz cups that they grew up in inside the 12"x 12" screen cage, so males may have a chance to escape whilst .. Keep houseflies / hydei available and mist as it encourages mating.....and they like to drink water sometimes.
Thanks for your good advice. I'll try it. I have noticed with higher the temp. the brown vomiting condition disappeared completely. 'Don't touch me there' by the Tubes also protect against COVID 2. (so far)
I keep all at 75F - 83F. In Arizona humidity can fall into single digits. Without misting, a humidifier, and a plastic blue plate with water under the screen cage mis-molting happens. But I'm still learning. Hope this helps.