When maggots or larvae of other insect species reach their teenage moments between their carefree meat devouring days as maggots and their future life as horrible buzzing fruit devouring monster with wings, they encase themselves in a protective cacoon much like that. Inside the cocoon the maggots basically liquify and rearrange themselves into the adult body plan. So I'd imagine you just murdered an insect teenager. can't specify more accurately what kind of insect though, sorry.