The emptied husk of a dog day cicada (Neotibicen). This is the final form of the underground nymph stage of these annual cicadas, which spend four to five years underground sucking on plant roots, counting the days. They’re “annual” because there’s a brood or cohort every year. 
This is split open and hollow inside now, because the adult form has emerged to make its way up into the tree for a summer of, ideally, love.
There were nine of these on the bole of this fat beech in Green-Wood a week ago. That’s a lot. Other beeches had one or a few on them. Do they like beeches in particular, or are these exuviae just easier to spot on the silvery-gray bark?
Backyard and Beyond 
What a beautiful pattern on the Beech Tree!!!!!!!! Of course, the cicada is beautiful, too. What a life to live underground for so long. There is a metaphor there.
I found a cicada shell a while back and it was so much smaller than cicadas are that I looked online and saw a great video of a cicada emerging from the little shell. Amazing! What is even more amazing was that I found links to cicada shells being sold on Etsy! Who knew. I actually never tried to buy them, so must be a market if people go to the trouble to post items for sale.
It is remarkable. Similar to dragonflies and damselflies emerging their aquatic nymph states; or butterfly emerging form cocoon/chrysalis. They’re always quite vulnerable at first, wings crumpled up, exoskeleton still soft.