Yup looks like a cicada shell to me. Ever see a live one? They are huge and are one of the ugliest insects I've ever seen and have a loud ear piercing call. Sometimes they are mistakenly referred to as locusts. Locusts are a similar insect native to the Middle East and Africa. I found about 5 or 6 of the emply shells clinging to my leaves already this year with no apparant damage. They usually only emerge every 13 or 17 years in large numbers, but every once in awhile there will be a small hatching. Last big outbreak where I live was in the summer of 2004 I believe. Maybe some of you can remember, they were everywhere. I think this might be one of the small years. I know that can wreak havoc on certain species of plants, but I'm not sure about cannabis.