Depending on the what stage of mantis you have, generally, smaller nymphs require food more often than larger nymphs as the smaller one grow very fast and molt often. without food/water, L1-L2 will not likely to stay longer than 1 week. larger nymphs/adult can survive w/o food/water for 2-3 weeks. It is never good to let mantis starve eventhough they can handle it, i realized that frequency of mismolting increases with less nutrition/poorly fed mantis. I was away from home for a week recently, what i did was adding some fly pupa in the mantis cage a day before leaving home, and remove more pupa from the fridge and add them in the cage with plenty of live flies prior to leaving. that way, you can ensure food supply for a good week as pupa will continue to pupate over next few days. Also, remember to have food not only for the mantis, but for the feeder as well, so a cup of honey water will help to extend the life of your feeders besides better nutrition for your mantis. For small nymph (L1-L3) which i kept together in groups, i have flyable fruit flies with honey watre in the cage, the fruit flies will last for a week no problem. Obviously, this work for a short period of time (1-2 week). The best way is still have someone to care for. Have any of your family member drop few pupa in the cage everyday, it shouldn't be too difficult, unless you have loads of mantis like myself. Also, if you are leaving for longer period of time, you might want to consider leaving the blue bottle grubs in a pan and let it pupate, which will take a longer time to hatch.
