This is definitely a squirrel, they like to fray the insulation, I can assure you that. I recommend you to get rid of it as soon as possible, otherwise you can remain without insulation, trust me, I know from my personal experience that squirrels are not so friendly as they look. Try to place some traps. In case they don't work, you can use the help of a squirrel removal company, those guys will definitely know what to do. Hope you will manage to solve this problem. Wish you good luck.