I was gone for a month. When I came back, I found this thing on my window sill. It's super tough and I don't know how to remove this. Can someone please tell me how to safely remove whatever this structure is?

I was gone for a month. When I came back, I found this thing on my window sill. It's super tough and I don't know how to remove this. Can someone please tell me how to safely remove whatever this structure is?