Okay so has anyone tried to sex a mantis with like a magnifying glass or something but it wouldn't stay still? Well I have news for you. Examination of shed skin is a great way of sexing your mantis. I usually sex my mantids by looking at the end of the abdomen and seeing whether or not there is a genital cup, or an ovipositor at the end. This is good for species like Creobroter, whose segments are especially small and hard to properly count. I can sex a mantis as early as L3 with this method. If you can't view the end of the abdomen on a live mantis because it's so active, use a shed skin, as long as the mantis was at least L3 before it shed the skin you examined, then you can use a magnifying glass or microscope to look at it. Also you might need something to hold it, as shed skin blows around with the lightest breath.