It is some kind of pupa. You could have left it in place.....what will hatch from this is some sort of moth or butterfly and neither will be harmful to the tree.

It is also very late in the season for this to be unhatched so maybe it is no longer viable. Being very hard would also support that premise.

That's a possibility as well - we don't have mantises here so not something I'd recognize :-) But if it is, that's a very beneficial insect to have in your garden. They are of no harm to the tree and will eat all manner of harmful insects and common plant bugs. They are garden good guys!!

If it is a praying mantis case it may not hatch till next year. I had 3 mantis nests last year and they didn't look exactly like that, but it did look similar. I don't know how much similarity there is in PM nests, it may be a different species that what I have here. could also be something similar to a PM, some sort of walking stick.

I would get a critter cage from a pet shop and let it hach...might be a beneficial insect.

Oops. I guess I should have asked before cutting it off, but I was trimming anyway and was afraid it might be harmful to the tree. It is still in the pile of cuttings in my yard, so maybe it will make it. We have many praying mantis' and more ladybugs than you can imagine, so lots of beneficial insects in our yard. Seems late in the season for anything to be hatching, though

It's absolutely a mantis egg case (ootheca). If I'm not mistaken, it's one from a native mantid and not the problematic Chinese mantid.

Mantid ootheca are made for overwintering; the tiny insects will hatch as the temperatures warm up in the spring. That's one reason why we shouldn't bring these inside....they will hatch in a warm house and then what? Eeek!

What do you think the little hatchlings will eat inside for the winter? Each other, and with great ferosity, lol.

That is a native mantis, the ones I had were the non-native Chinese Mantis. Are they harmful to the native species? Not sure if I should euthanize them or not. I did read they like to eat those nasty Chinese stink bugs though.