I went to feed the mantids this morning and for a moment thought some other bug had gotten in with one of them. During hatching I’ve had a few others end up loose in the house and found them wandering around later, so it’s not completely impossible:

mantis first molt

Nope, it’s just the first molting. That’s two weeks to the day from hatching. This was a bit of a surprise since I’ve read that they usually don’t eat leading up to it, but I haven’t noticed any fasting. It’s now a lighter color and definitely larger and lankier. Also a lot more skittish, which I guess is to be expected right afterward:

exoskeleton
l2 mantis