I never throw a cricket in and leave it. Not because anything bad happened to me per say, but because I read about these cases where crickets could eat or bite pets.
What I do is I feed a single cricket at a time. If the mantis doesn't even notice it, I'll take the cricket out and try again later. If the mantis hasn't eaten for a while, sometimes I'll hand feed the cricket, but I haven't needed to do this since November when I had the adult Chinese mantises.
This past week I got 6 crickets and fed 4 of them to my L5 African mantises. Since feeding them, the only one that looks like he might need to be fed again soon (with flies, not crickets) is Fortune. I have 2 crickets left as well.
I might wait until they are L6 to feed them crickets again, or maybe see if I can find smaller crickets than the ones at Petco. I'm still concerned that even when I make sure the mantis takes the cricket, that the cricket might bite at his raptorial arms and cause an injury of sort. So, even if the mantis catches and successfully starts devouring the cricket, I make sure the cricket is not in a position to be able to bite.
I also have videos of each mantis' first cricket.
Meek:
- Had the cricket in a locked position and ate it head first. If I ever feel that a cricket might pose some threat to my mantises with its mandibles, I would take the small forceps I have and squeeze its head while the mantis is feeding. I already know that they don't let go of their food very easily, which would help provide a counter force so I don't accidentally pull the cricket away (but sometimes I have to pull remaining food away so they don't over eat, did this with Kit and Angel for their first crickets and when I fed them house flies when they were L2 or L3 and realized that the flies were somewhat too big)